repl: add basic syntax highlighting

Signed-off-by: avivkeller <me@aviv.sh>
PR-URL: #64591
Backport-PR-URL: #65267
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>

Author: avivkeller

lib/internal/readline/interface.js

@@ -157,13 +157,15 @@ const kPreviousCursorCols = Symbol('_previousCursorCols');
 constkMultilineMove=Symbol('_multilineMove');
 constkPreviousPrevRows=Symbol('_previousPrevRows');
 constkAddNewLineOnTTY=Symbol('_addNewLineOnTTY');
+constkColorize=Symbol('_colorize');
 
 functionInterfaceConstructor(input,output,completer,terminal){
 this[kSawReturnAt]=0;
 // TODO(BridgeAR): Document this property. The name is not ideal, so we
 // might want to expose an alias and document that instead.
 this.isCompletionEnabled=true;
 this[kSawKeyPress]=false;
+this[kColorize]=undefined;
 this[kPreviousKey]=null;
 this.escapeCodeTimeout=ESCAPE_CODE_TIMEOUT;
 this.tabSize=8;
@@ -186,6 +188,7 @@ function InterfaceConstructor(input, output, completer, terminal) {
 consthistorySize=input.historySize;
 consthistory=input.history;
 constremoveHistoryDuplicates=input.removeHistoryDuplicates;
+this[kColorize]=input.colorize;
 
 if(input.tabSize!==undefined){
 validateUint32(input.tabSize,'tabSize',true);
@@ -523,15 +526,18 @@ class Interface extends InterfaceConstructor {
 if(this[kIsMultiline]){
 constlines=StringPrototypeSplit(this.line,'\n');
 // Write first line with normal prompt
-this[kWriteToOutput](this[kPrompt]+lines[0]);
+this[kWriteToOutput](this[kPrompt]+
+(this[kColorize]?.(lines[0])??lines[0]));
 
 // For continuation lines, add the "|" prefix
 for(leti=1;i<lines.length;i++){
-this[kWriteToOutput](`\n${kMultilinePrompt.description}`+lines[i]);
+this[kWriteToOutput](`\n${kMultilinePrompt.description}`+
+(this[kColorize]?.(lines[i])??lines[i]));
 }
 }else{
 // Write the prompt and the current buffer content.
-this[kWriteToOutput](line);
+this[kWriteToOutput](this[kPrompt]+
+(this[kColorize]?.(this.line)??this.line));
 }
 
 // Force terminal to allocate a new line
@@ -687,7 +693,11 @@ class Interface extends InterfaceConstructor {
 this.line+=c;
 }
 this.cursor+=c.length;
-this[kWriteToOutput](c);
+if(this[kColorize]===undefined){
+this[kWriteToOutput](c);
+}else{
+this[kRefreshLine]();
+}
 return;
 }
 if(this.cursor<this.line.length){
@@ -706,7 +716,7 @@ class Interface extends InterfaceConstructor {
 this.cursor+=c.length;
 constnewPos=this.getCursorPos();
 
-if(oldPos.rows<newPos.rows){
+if(oldPos.rows<newPos.rows||this[kColorize]!==undefined){
 this[kRefreshLine]();
 }else{
 this[kWriteToOutput](c);

lib/internal/repl/highlight.js

@@ -0,0 +1,89 @@
+'use strict';
+
+const{
+ FunctionPrototypeBind,
+ StringPrototypeSlice,
+}=primordials;
+
+const{ stylizeWithColor }=require('internal/util/inspect');
+const{ Parser }=require('internal/deps/acorn/acorn/dist/acorn');
+
+consttokenizer=FunctionPrototypeBind(Parser.tokenizer,Parser);
+
+functiontokenStyle(token){
+const{ label, keyword }=token.type;
+
+if(keyword!==undefined){
+if(label==='true'||label==='false')return'boolean';
+if(label==='null')return'null';
+if(label==='import'||label==='export')return'module';
+return'special';
+}
+
+switch(label){
+case'name':
+switch(token.value){
+case'undefined':
+return'undefined';
+case'NaN':
+case'Infinity':
+return'number';
+case'Symbol':
+return'symbol';
+case'Date':
+return'date';
+default:
+returnundefined;
+}
+case'num':
+return'number';
+case'bigint':
+return'bigint';
+case'string':
+case'template':
+case'`':
+return'string';
+case'regexp':
+return'regexp';
+default:
+returnundefined;
+}
+}
+
+functionhighlight(code){
+if(code.length===0)returncode;
+
+letresult='';
+letoffset=0;
+functionwrite(start,end,style){
+result+=
+StringPrototypeSlice(code,offset,start)+
+stylizeWithColor(StringPrototypeSlice(code,start,end),style);
+offset=end;
+}
+
+try{
+constiterator=tokenizer(code,{
+__proto__: null,
+allowHashBang: true,
+ecmaVersion: 'latest',
+onComment(_block,_text,start,end){
+write(start,end,'undefined');
+},
+});
+
+for(consttokenofiterator){
+conststyle=tokenStyle(token);
+if(style!==undefined){
+write(token.start,token.end,style);
+}
+}
+}catch{
+// Acorn throws for unfinished strings, templates, and comments. Tokens and
+// comments reported before that point are still useful while typing.
+}
+
+returnresult+StringPrototypeSlice(code,offset);
+}
+
+module.exports={ highlight };

lib/internal/util/inspect.js

@@ -3057,6 +3057,7 @@ module.exports = {
  identicalSequenceRange,
  inspect,
  inspectDefaultOptions,
+ stylizeWithColor,
  format,
  formatWithOptions,
  getStringWidth,

lib/repl.js

@@ -109,6 +109,7 @@ const {
 }=require('internal/readline/utils');
 const{ Console }=require('console');
 const{ shouldColorize }=require('internal/util/colors');
+const{ highlight }=require('internal/repl/highlight');
 constCJSModule=require('internal/modules/cjs/loader').Module;
 const{ AsyncLocalStorage }=require('async_hooks');
 letdebug=require('internal/util/debuglog').debuglog('repl',(fn)=>{
@@ -326,6 +327,7 @@ class REPLServer extends Interface {
 terminal: options.terminal,
 historySize: options.historySize,
  prompt,
+colorize: options.useColors ? highlight : undefined,
 });
 
 ObjectDefineProperty(this,'inputStream',{

test/parallel/test-repl-highlight.js

@@ -0,0 +1,61 @@
+// Flags: --expose-internals
+'use strict';
+
+constcommon=require('../common');
+constassert=require('assert');
+const{ inspect, stripVTControlCharacters }=require('util');
+constArrayStream=require('../common/arraystream');
+const{ highlight }=require('internal/repl/highlight');
+const{ REPLServer }=require('repl');
+
+common.skipIfInspectorDisabled();
+
+assert.strictEqual(stripVTControlCharacters(highlight(
+'const /* comment */ answer = 42; // comment',
+)),'const /* comment */ answer = 42; // comment');
+
+assert.strictEqual(
+highlight('const value = "text"'),
+`\u001b[${inspect.colors.cyan[0]}mconst\u001b[${inspect.colors.cyan[1]}m value = `+
+`\u001b[${inspect.colors.green[0]}m"text"\u001b[${inspect.colors.green[1]}m`,
+);
+
+for(constsourceof[
+'undefined',
+'NaN',
+'Infinity',
+'Symbol.iterator',
+'Date.now()',
+'true',
+'null',
+'1n',
+'/regexp/u',
+'import("node:fs")',
+]){
+assert.notStrictEqual(highlight(source),source);
+}
+
+// Incomplete source is expected while the user is typing.
+highlight('const value = "');
+
+{
+constinput=newArrayStream();
+constoutput=newArrayStream();
+letrendered='';
+output.write=(chunk)=>{
+rendered+=chunk;
+};
+
+constrepl=newREPLServer({
+ input,
+ output,
+prompt: '',
+terminal: true,
+useColors: false,
+});
+rendered='';
+repl.write('const');
+
+assert.strictEqual(rendered,'const');
+repl.close();
+}

test/parallel/test-repl-multiline.js

@@ -2,23 +2,24 @@
 constcommon=require('../common');
 constassert=require('assert');
 const{ startNewREPLServer }=require('../common/repl');
+const{ stripVTControlCharacters }=require('util');
 
 constinput=['const foo = {','};','foo'];
 
 functionrun({ useColors }){
 const{ replServer, output }=startNewREPLServer({ useColors });
 
 replServer.on('exit',common.mustCall(()=>{
-constactual=output.accumulator.split('\n');
+// The output contains various escape codes, including
+// screen clears and others, so we trim them all to
+// simplify this test.
+constactual=stripVTControlCharacters(output.accumulator);
 
-// Validate the output, which contains terminal escape codes.
-assert.strictEqual(actual.length,6);
-assert.ok(actual[0].endsWith(input[0]));
-assert.ok(actual[1].includes('| '));
-assert.ok(actual[1].endsWith(input[1]));
-assert.ok(actual[2].includes('undefined'));
-assert.ok(actual[3].endsWith(input[2]));
-assert.strictEqual(actual[4],'{}');
+constfirstStatementIdx=actual.indexOf(input.slice(0,1).join('\n| '));
+assert(firstStatementIdx>-1);
+
+assert(actual.slice(firstStatementIdx).includes('undefined'));
+assert(actual.slice(firstStatementIdx).includes('foo'));
 }));
 
 input.forEach((line)=>replServer.write(`${line}\n`));

test/parallel/test-repl-preview-newlines.js

@@ -6,7 +6,14 @@ const { startNewREPLServer } = require('../common/repl');
 
 common.skipIfInspectorDisabled();
 
-const{ input, output }=startNewREPLServer({useColors: true});
+// Ignore terminal settings so the preview remains active under TERM=dumb.
+process.env.TERM='';
+
+// Keep syntax highlighting out of this test so it only covers preview layout.
+// Preview and result colors are enabled after readline is initialized.
+const{ input, output, replServer }=startNewREPLServer({useColors: false});
+replServer.useColors=true;
+replServer.writer.options.colors=true;
 
 output.accumulator='';
 

test/parallel/test-repl-preview-without-inspector.js

@@ -69,9 +69,13 @@ const repl = new REPLServer({
 prompt: PROMPT,
 stream: newREPLStream(),
 ignoreUndefined: true,
-useColors: true,
+// Keep syntax highlighting out of these preview transcript assertions.
+// Preview and result colors are enabled after readline is initialized.
+useColors: false,
 terminal: true,
 });
+repl.useColors=true;
+repl.writer.options.colors=true;
 
 repl.inputStream.run([
 'function foo(x) { return x; }',

test/parallel/test-repl-preview.js

@@ -61,9 +61,13 @@ async function tests(options) {
 prompt: PROMPT,
 stream: newREPLStream(),
 ignoreUndefined: true,
-useColors: true,
+// Keep syntax highlighting out of these preview transcript assertions.
+// Preview and result colors are enabled after readline is initialized.
+useColors: false,
  ...options
 });
+repl.useColors=true;
+repl.writer.options.colors=true;
 
 repl.inputStream.run([
 'function foo(x) { return x; }',

test/parallel/test-repl-reverse-search.js

@@ -329,7 +329,9 @@ function runTest() {
 }),
 completer: opts.completer,
  prompt,
-useColors: opts.useColors||false,
+// Keep syntax highlighting out of the reverse-search transcript. Result
+// colors are enabled below after readline has been initialized.
+useColors: false,
 terminal: true
 },common.mustCall((err,repl)=>{
 if(err){
@@ -351,6 +353,11 @@ function runTest() {
 setImmediate(runTestWrap,true);
 }));
 
+if(opts.useColors){
+repl.useColors=true;
+repl.writer.options.colors=true;
+}
+
 if(opts.columns){
 Object.defineProperty(repl,'columns',{
 value: opts.columns,

lib/internal/readline/interface.js

@@ -157,13 +157,15 @@ const kPreviousCursorCols = Symbol('_previousCursorCols');
 constkMultilineMove=Symbol('_multilineMove');
 constkPreviousPrevRows=Symbol('_previousPrevRows');
 constkAddNewLineOnTTY=Symbol('_addNewLineOnTTY');
+constkColorize=Symbol('_colorize');
 
 functionInterfaceConstructor(input,output,completer,terminal){
 this[kSawReturnAt]=0;
 // TODO(BridgeAR): Document this property. The name is not ideal, so we
 // might want to expose an alias and document that instead.
 this.isCompletionEnabled=true;
 this[kSawKeyPress]=false;
+this[kColorize]=undefined;
 this[kPreviousKey]=null;
 this.escapeCodeTimeout=ESCAPE_CODE_TIMEOUT;
 this.tabSize=8;
@@ -186,6 +188,7 @@ function InterfaceConstructor(input, output, completer, terminal) {
 consthistorySize=input.historySize;
 consthistory=input.history;
 constremoveHistoryDuplicates=input.removeHistoryDuplicates;
+this[kColorize]=input.colorize;
 
 if(input.tabSize!==undefined){
 validateUint32(input.tabSize,'tabSize',true);
@@ -523,15 +526,18 @@ class Interface extends InterfaceConstructor {
 if(this[kIsMultiline]){
 constlines=StringPrototypeSplit(this.line,'\n');
 // Write first line with normal prompt
-this[kWriteToOutput](this[kPrompt]+lines[0]);
+this[kWriteToOutput](this[kPrompt]+
+(this[kColorize]?.(lines[0])??lines[0]));
 
 // For continuation lines, add the "|" prefix
 for(leti=1;i<lines.length;i++){
-this[kWriteToOutput](`\n${kMultilinePrompt.description}`+lines[i]);
+this[kWriteToOutput](`\n${kMultilinePrompt.description}`+
+(this[kColorize]?.(lines[i])??lines[i]));
 }
 }else{
 // Write the prompt and the current buffer content.
-this[kWriteToOutput](line);
+this[kWriteToOutput](this[kPrompt]+
+(this[kColorize]?.(this.line)??this.line));
 }
 
 // Force terminal to allocate a new line
@@ -687,7 +693,11 @@ class Interface extends InterfaceConstructor {
 this.line+=c;
 }
 this.cursor+=c.length;
-this[kWriteToOutput](c);
+if(this[kColorize]===undefined){
+this[kWriteToOutput](c);
+}else{
+this[kRefreshLine]();
+}
 return;
 }
 if(this.cursor<this.line.length){
@@ -706,7 +716,7 @@ class Interface extends InterfaceConstructor {
 this.cursor+=c.length;
 constnewPos=this.getCursorPos();
 
-if(oldPos.rows<newPos.rows){
+if(oldPos.rows<newPos.rows||this[kColorize]!==undefined){
 this[kRefreshLine]();
 }else{
 this[kWriteToOutput](c);

lib/internal/repl/highlight.js

@@ -0,0 +1,89 @@
+'use strict';
+
+const{
+ FunctionPrototypeBind,
+ StringPrototypeSlice,
+}=primordials;
+
+const{ stylizeWithColor }=require('internal/util/inspect');
+const{ Parser }=require('internal/deps/acorn/acorn/dist/acorn');
+
+consttokenizer=FunctionPrototypeBind(Parser.tokenizer,Parser);
+
+functiontokenStyle(token){
+const{ label, keyword }=token.type;
+
+if(keyword!==undefined){
+if(label==='true'||label==='false')return'boolean';
+if(label==='null')return'null';
+if(label==='import'||label==='export')return'module';
+return'special';
+}
+
+switch(label){
+case'name':
+switch(token.value){
+case'undefined':
+return'undefined';
+case'NaN':
+case'Infinity':
+return'number';
+case'Symbol':
+return'symbol';
+case'Date':
+return'date';
+default:
+returnundefined;
+}
+case'num':
+return'number';
+case'bigint':
+return'bigint';
+case'string':
+case'template':
+case'`':
+return'string';
+case'regexp':
+return'regexp';
+default:
+returnundefined;
+}
+}
+
+functionhighlight(code){
+if(code.length===0)returncode;
+
+letresult='';
+letoffset=0;
+functionwrite(start,end,style){
+result+=
+StringPrototypeSlice(code,offset,start)+
+stylizeWithColor(StringPrototypeSlice(code,start,end),style);
+offset=end;
+}
+
+try{
+constiterator=tokenizer(code,{
+__proto__: null,
+allowHashBang: true,
+ecmaVersion: 'latest',
+onComment(_block,_text,start,end){
+write(start,end,'undefined');
+},
+});
+
+for(consttokenofiterator){
+conststyle=tokenStyle(token);
+if(style!==undefined){
+write(token.start,token.end,style);
+}
+}
+}catch{
+// Acorn throws for unfinished strings, templates, and comments. Tokens and
+// comments reported before that point are still useful while typing.
+}
+
+returnresult+StringPrototypeSlice(code,offset);
+}
+
+module.exports={ highlight };

lib/internal/util/inspect.js

@@ -3057,6 +3057,7 @@ module.exports = {
  identicalSequenceRange,
  inspect,
  inspectDefaultOptions,
+ stylizeWithColor,
  format,
  formatWithOptions,
  getStringWidth,

lib/repl.js

@@ -109,6 +109,7 @@ const {
 }=require('internal/readline/utils');
 const{ Console }=require('console');
 const{ shouldColorize }=require('internal/util/colors');
+const{ highlight }=require('internal/repl/highlight');
 constCJSModule=require('internal/modules/cjs/loader').Module;
 const{ AsyncLocalStorage }=require('async_hooks');
 letdebug=require('internal/util/debuglog').debuglog('repl',(fn)=>{
@@ -326,6 +327,7 @@ class REPLServer extends Interface {
 terminal: options.terminal,
 historySize: options.historySize,
  prompt,
+colorize: options.useColors ? highlight : undefined,
 });
 
 ObjectDefineProperty(this,'inputStream',{

test/parallel/test-repl-highlight.js

@@ -0,0 +1,61 @@
+// Flags: --expose-internals
+'use strict';
+
+constcommon=require('../common');
+constassert=require('assert');
+const{ inspect, stripVTControlCharacters }=require('util');
+constArrayStream=require('../common/arraystream');
+const{ highlight }=require('internal/repl/highlight');
+const{ REPLServer }=require('repl');
+
+common.skipIfInspectorDisabled();
+
+assert.strictEqual(stripVTControlCharacters(highlight(
+'const /* comment */ answer = 42; // comment',
+)),'const /* comment */ answer = 42; // comment');
+
+assert.strictEqual(
+highlight('const value = "text"'),
+`\u001b[${inspect.colors.cyan[0]}mconst\u001b[${inspect.colors.cyan[1]}m value = `+
+`\u001b[${inspect.colors.green[0]}m"text"\u001b[${inspect.colors.green[1]}m`,
+);
+
+for(constsourceof[
+'undefined',
+'NaN',
+'Infinity',
+'Symbol.iterator',
+'Date.now()',
+'true',
+'null',
+'1n',
+'/regexp/u',
+'import("node:fs")',
+]){
+assert.notStrictEqual(highlight(source),source);
+}
+
+// Incomplete source is expected while the user is typing.
+highlight('const value = "');
+
+{
+constinput=newArrayStream();
+constoutput=newArrayStream();
+letrendered='';
+output.write=(chunk)=>{
+rendered+=chunk;
+};
+
+constrepl=newREPLServer({
+ input,
+ output,
+prompt: '',
+terminal: true,
+useColors: false,
+});
+rendered='';
+repl.write('const');
+
+assert.strictEqual(rendered,'const');
+repl.close();
+}

test/parallel/test-repl-multiline.js

@@ -2,23 +2,24 @@
 constcommon=require('../common');
 constassert=require('assert');
 const{ startNewREPLServer }=require('../common/repl');
+const{ stripVTControlCharacters }=require('util');
 
 constinput=['const foo = {','};','foo'];
 
 functionrun({ useColors }){
 const{ replServer, output }=startNewREPLServer({ useColors });
 
 replServer.on('exit',common.mustCall(()=>{
-constactual=output.accumulator.split('\n');
+// The output contains various escape codes, including
+// screen clears and others, so we trim them all to
+// simplify this test.
+constactual=stripVTControlCharacters(output.accumulator);
 
-// Validate the output, which contains terminal escape codes.
-assert.strictEqual(actual.length,6);
-assert.ok(actual[0].endsWith(input[0]));
-assert.ok(actual[1].includes('| '));
-assert.ok(actual[1].endsWith(input[1]));
-assert.ok(actual[2].includes('undefined'));
-assert.ok(actual[3].endsWith(input[2]));
-assert.strictEqual(actual[4],'{}');
+constfirstStatementIdx=actual.indexOf(input.slice(0,1).join('\n| '));
+assert(firstStatementIdx>-1);
+
+assert(actual.slice(firstStatementIdx).includes('undefined'));
+assert(actual.slice(firstStatementIdx).includes('foo'));
 }));
 
 input.forEach((line)=>replServer.write(`${line}\n`));

test/parallel/test-repl-preview-newlines.js

@@ -6,7 +6,14 @@ const { startNewREPLServer } = require('../common/repl');
 
 common.skipIfInspectorDisabled();
 
-const{ input, output }=startNewREPLServer({useColors: true});
+// Ignore terminal settings so the preview remains active under TERM=dumb.
+process.env.TERM='';
+
+// Keep syntax highlighting out of this test so it only covers preview layout.
+// Preview and result colors are enabled after readline is initialized.
+const{ input, output, replServer }=startNewREPLServer({useColors: false});
+replServer.useColors=true;
+replServer.writer.options.colors=true;
 
 output.accumulator='';
 

test/parallel/test-repl-preview-without-inspector.js

@@ -69,9 +69,13 @@ const repl = new REPLServer({
 prompt: PROMPT,
 stream: newREPLStream(),
 ignoreUndefined: true,
-useColors: true,
+// Keep syntax highlighting out of these preview transcript assertions.
+// Preview and result colors are enabled after readline is initialized.
+useColors: false,
 terminal: true,
 });
+repl.useColors=true;
+repl.writer.options.colors=true;
 
 repl.inputStream.run([
 'function foo(x) { return x; }',

test/parallel/test-repl-preview.js

@@ -61,9 +61,13 @@ async function tests(options) {
 prompt: PROMPT,
 stream: newREPLStream(),
 ignoreUndefined: true,
-useColors: true,
+// Keep syntax highlighting out of these preview transcript assertions.
+// Preview and result colors are enabled after readline is initialized.
+useColors: false,
  ...options
 });
+repl.useColors=true;
+repl.writer.options.colors=true;
 
 repl.inputStream.run([
 'function foo(x) { return x; }',

test/parallel/test-repl-reverse-search.js

@@ -329,7 +329,9 @@ function runTest() {
 }),
 completer: opts.completer,
  prompt,
-useColors: opts.useColors||false,
+// Keep syntax highlighting out of the reverse-search transcript. Result
+// colors are enabled below after readline has been initialized.
+useColors: false,
 terminal: true
 },common.mustCall((err,repl)=>{
 if(err){
@@ -351,6 +353,11 @@ function runTest() {
 setImmediate(runTestWrap,true);
 }));
 
+if(opts.useColors){
+repl.useColors=true;
+repl.writer.options.colors=true;
+}
+
 if(opts.columns){
 Object.defineProperty(repl,'columns',{
 value: opts.columns,

lib/internal/readline/interface.js

@@ -157,13 +157,15 @@ const kPreviousCursorCols = Symbol('_previousCursorCols');
 constkMultilineMove=Symbol('_multilineMove');
 constkPreviousPrevRows=Symbol('_previousPrevRows');
 constkAddNewLineOnTTY=Symbol('_addNewLineOnTTY');
+constkColorize=Symbol('_colorize');
 
 functionInterfaceConstructor(input,output,completer,terminal){
 this[kSawReturnAt]=0;
 // TODO(BridgeAR): Document this property. The name is not ideal, so we
 // might want to expose an alias and document that instead.
 this.isCompletionEnabled=true;
 this[kSawKeyPress]=false;
+this[kColorize]=undefined;
 this[kPreviousKey]=null;
 this.escapeCodeTimeout=ESCAPE_CODE_TIMEOUT;
 this.tabSize=8;
@@ -186,6 +188,7 @@ function InterfaceConstructor(input, output, completer, terminal) {
 consthistorySize=input.historySize;
 consthistory=input.history;
 constremoveHistoryDuplicates=input.removeHistoryDuplicates;
+this[kColorize]=input.colorize;
 
 if(input.tabSize!==undefined){
 validateUint32(input.tabSize,'tabSize',true);
@@ -523,15 +526,18 @@ class Interface extends InterfaceConstructor {
 if(this[kIsMultiline]){
 constlines=StringPrototypeSplit(this.line,'\n');
 // Write first line with normal prompt
-this[kWriteToOutput](this[kPrompt]+lines[0]);
+this[kWriteToOutput](this[kPrompt]+
+(this[kColorize]?.(lines[0])??lines[0]));
 
 // For continuation lines, add the "|" prefix
 for(leti=1;i<lines.length;i++){
-this[kWriteToOutput](`\n${kMultilinePrompt.description}`+lines[i]);
+this[kWriteToOutput](`\n${kMultilinePrompt.description}`+
+(this[kColorize]?.(lines[i])??lines[i]));
 }
 }else{
 // Write the prompt and the current buffer content.
-this[kWriteToOutput](line);
+this[kWriteToOutput](this[kPrompt]+
+(this[kColorize]?.(this.line)??this.line));
 }
 
 // Force terminal to allocate a new line
@@ -687,7 +693,11 @@ class Interface extends InterfaceConstructor {
 this.line+=c;
 }
 this.cursor+=c.length;
-this[kWriteToOutput](c);
+if(this[kColorize]===undefined){
+this[kWriteToOutput](c);
+}else{
+this[kRefreshLine]();
+}
 return;
 }
 if(this.cursor<this.line.length){
@@ -706,7 +716,7 @@ class Interface extends InterfaceConstructor {
 this.cursor+=c.length;
 constnewPos=this.getCursorPos();
 
-if(oldPos.rows<newPos.rows){
+if(oldPos.rows<newPos.rows||this[kColorize]!==undefined){
 this[kRefreshLine]();
 }else{
 this[kWriteToOutput](c);

lib/internal/repl/highlight.js

@@ -0,0 +1,89 @@
+'use strict';
+
+const{
+ FunctionPrototypeBind,
+ StringPrototypeSlice,
+}=primordials;
+
+const{ stylizeWithColor }=require('internal/util/inspect');
+const{ Parser }=require('internal/deps/acorn/acorn/dist/acorn');
+
+consttokenizer=FunctionPrototypeBind(Parser.tokenizer,Parser);
+
+functiontokenStyle(token){
+const{ label, keyword }=token.type;
+
+if(keyword!==undefined){
+if(label==='true'||label==='false')return'boolean';
+if(label==='null')return'null';
+if(label==='import'||label==='export')return'module';
+return'special';
+}
+
+switch(label){
+case'name':
+switch(token.value){
+case'undefined':
+return'undefined';
+case'NaN':
+case'Infinity':
+return'number';
+case'Symbol':
+return'symbol';
+case'Date':
+return'date';
+default:
+returnundefined;
+}
+case'num':
+return'number';
+case'bigint':
+return'bigint';
+case'string':
+case'template':
+case'`':
+return'string';
+case'regexp':
+return'regexp';
+default:
+returnundefined;
+}
+}
+
+functionhighlight(code){
+if(code.length===0)returncode;
+
+letresult='';
+letoffset=0;
+functionwrite(start,end,style){
+result+=
+StringPrototypeSlice(code,offset,start)+
+stylizeWithColor(StringPrototypeSlice(code,start,end),style);
+offset=end;
+}
+
+try{
+constiterator=tokenizer(code,{
+__proto__: null,
+allowHashBang: true,
+ecmaVersion: 'latest',
+onComment(_block,_text,start,end){
+write(start,end,'undefined');
+},
+});
+
+for(consttokenofiterator){
+conststyle=tokenStyle(token);
+if(style!==undefined){
+write(token.start,token.end,style);
+}
+}
+}catch{
+// Acorn throws for unfinished strings, templates, and comments. Tokens and
+// comments reported before that point are still useful while typing.
+}
+
+returnresult+StringPrototypeSlice(code,offset);
+}
+
+module.exports={ highlight };

lib/internal/util/inspect.js

@@ -3057,6 +3057,7 @@ module.exports = {
  identicalSequenceRange,
  inspect,
  inspectDefaultOptions,
+ stylizeWithColor,
  format,
  formatWithOptions,
  getStringWidth,

lib/repl.js

@@ -109,6 +109,7 @@ const {
 }=require('internal/readline/utils');
 const{ Console }=require('console');
 const{ shouldColorize }=require('internal/util/colors');
+const{ highlight }=require('internal/repl/highlight');
 constCJSModule=require('internal/modules/cjs/loader').Module;
 const{ AsyncLocalStorage }=require('async_hooks');
 letdebug=require('internal/util/debuglog').debuglog('repl',(fn)=>{
@@ -326,6 +327,7 @@ class REPLServer extends Interface {
 terminal: options.terminal,
 historySize: options.historySize,
  prompt,
+colorize: options.useColors ? highlight : undefined,
 });
 
 ObjectDefineProperty(this,'inputStream',{

test/parallel/test-repl-highlight.js

@@ -0,0 +1,61 @@
+// Flags: --expose-internals
+'use strict';
+
+constcommon=require('../common');
+constassert=require('assert');
+const{ inspect, stripVTControlCharacters }=require('util');
+constArrayStream=require('../common/arraystream');
+const{ highlight }=require('internal/repl/highlight');
+const{ REPLServer }=require('repl');
+
+common.skipIfInspectorDisabled();
+
+assert.strictEqual(stripVTControlCharacters(highlight(
+'const /* comment */ answer = 42; // comment',
+)),'const /* comment */ answer = 42; // comment');
+
+assert.strictEqual(
+highlight('const value = "text"'),
+`\u001b[${inspect.colors.cyan[0]}mconst\u001b[${inspect.colors.cyan[1]}m value = `+
+`\u001b[${inspect.colors.green[0]}m"text"\u001b[${inspect.colors.green[1]}m`,
+);
+
+for(constsourceof[
+'undefined',
+'NaN',
+'Infinity',
+'Symbol.iterator',
+'Date.now()',
+'true',
+'null',
+'1n',
+'/regexp/u',
+'import("node:fs")',
+]){
+assert.notStrictEqual(highlight(source),source);
+}
+
+// Incomplete source is expected while the user is typing.
+highlight('const value = "');
+
+{
+constinput=newArrayStream();
+constoutput=newArrayStream();
+letrendered='';
+output.write=(chunk)=>{
+rendered+=chunk;
+};
+
+constrepl=newREPLServer({
+ input,
+ output,
+prompt: '',
+terminal: true,
+useColors: false,
+});
+rendered='';
+repl.write('const');
+
+assert.strictEqual(rendered,'const');
+repl.close();
+}

test/parallel/test-repl-multiline.js

@@ -2,23 +2,24 @@
 constcommon=require('../common');
 constassert=require('assert');
 const{ startNewREPLServer }=require('../common/repl');
+const{ stripVTControlCharacters }=require('util');
 
 constinput=['const foo = {','};','foo'];
 
 functionrun({ useColors }){
 const{ replServer, output }=startNewREPLServer({ useColors });
 
 replServer.on('exit',common.mustCall(()=>{
-constactual=output.accumulator.split('\n');
+// The output contains various escape codes, including
+// screen clears and others, so we trim them all to
+// simplify this test.
+constactual=stripVTControlCharacters(output.accumulator);
 
-// Validate the output, which contains terminal escape codes.
-assert.strictEqual(actual.length,6);
-assert.ok(actual[0].endsWith(input[0]));
-assert.ok(actual[1].includes('| '));
-assert.ok(actual[1].endsWith(input[1]));
-assert.ok(actual[2].includes('undefined'));
-assert.ok(actual[3].endsWith(input[2]));
-assert.strictEqual(actual[4],'{}');
+constfirstStatementIdx=actual.indexOf(input.slice(0,1).join('\n| '));
+assert(firstStatementIdx>-1);
+
+assert(actual.slice(firstStatementIdx).includes('undefined'));
+assert(actual.slice(firstStatementIdx).includes('foo'));
 }));
 
 input.forEach((line)=>replServer.write(`${line}\n`));

test/parallel/test-repl-preview-newlines.js

@@ -6,7 +6,14 @@ const { startNewREPLServer } = require('../common/repl');
 
 common.skipIfInspectorDisabled();
 
-const{ input, output }=startNewREPLServer({useColors: true});
+// Ignore terminal settings so the preview remains active under TERM=dumb.
+process.env.TERM='';
+
+// Keep syntax highlighting out of this test so it only covers preview layout.
+// Preview and result colors are enabled after readline is initialized.
+const{ input, output, replServer }=startNewREPLServer({useColors: false});
+replServer.useColors=true;
+replServer.writer.options.colors=true;
 
 output.accumulator='';
 

test/parallel/test-repl-preview-without-inspector.js

@@ -69,9 +69,13 @@ const repl = new REPLServer({
 prompt: PROMPT,
 stream: newREPLStream(),
 ignoreUndefined: true,
-useColors: true,
+// Keep syntax highlighting out of these preview transcript assertions.
+// Preview and result colors are enabled after readline is initialized.
+useColors: false,
 terminal: true,
 });
+repl.useColors=true;
+repl.writer.options.colors=true;
 
 repl.inputStream.run([
 'function foo(x) { return x; }',

test/parallel/test-repl-preview.js

@@ -61,9 +61,13 @@ async function tests(options) {
 prompt: PROMPT,
 stream: newREPLStream(),
 ignoreUndefined: true,
-useColors: true,
+// Keep syntax highlighting out of these preview transcript assertions.
+// Preview and result colors are enabled after readline is initialized.
+useColors: false,
  ...options
 });
+repl.useColors=true;
+repl.writer.options.colors=true;
 
 repl.inputStream.run([
 'function foo(x) { return x; }',

test/parallel/test-repl-reverse-search.js

@@ -329,7 +329,9 @@ function runTest() {
 }),
 completer: opts.completer,
  prompt,
-useColors: opts.useColors||false,
+// Keep syntax highlighting out of the reverse-search transcript. Result
+// colors are enabled below after readline has been initialized.
+useColors: false,
 terminal: true
 },common.mustCall((err,repl)=>{
 if(err){
@@ -351,6 +353,11 @@ function runTest() {
 setImmediate(runTestWrap,true);
 }));
 
+if(opts.useColors){
+repl.useColors=true;
+repl.writer.options.colors=true;
+}
+
 if(opts.columns){
 Object.defineProperty(repl,'columns',{
 value: opts.columns,

lib/internal/readline/interface.js

@@ -157,13 +157,15 @@ const kPreviousCursorCols = Symbol('_previousCursorCols');
 constkMultilineMove=Symbol('_multilineMove');
 constkPreviousPrevRows=Symbol('_previousPrevRows');
 constkAddNewLineOnTTY=Symbol('_addNewLineOnTTY');
+constkColorize=Symbol('_colorize');
 
 functionInterfaceConstructor(input,output,completer,terminal){
 this[kSawReturnAt]=0;
 // TODO(BridgeAR): Document this property. The name is not ideal, so we
 // might want to expose an alias and document that instead.
 this.isCompletionEnabled=true;
 this[kSawKeyPress]=false;
+this[kColorize]=undefined;
 this[kPreviousKey]=null;
 this.escapeCodeTimeout=ESCAPE_CODE_TIMEOUT;
 this.tabSize=8;
@@ -186,6 +188,7 @@ function InterfaceConstructor(input, output, completer, terminal) {
 consthistorySize=input.historySize;
 consthistory=input.history;
 constremoveHistoryDuplicates=input.removeHistoryDuplicates;
+this[kColorize]=input.colorize;
 
 if(input.tabSize!==undefined){
 validateUint32(input.tabSize,'tabSize',true);
@@ -523,15 +526,18 @@ class Interface extends InterfaceConstructor {
 if(this[kIsMultiline]){
 constlines=StringPrototypeSplit(this.line,'\n');
 // Write first line with normal prompt
-this[kWriteToOutput](this[kPrompt]+lines[0]);
+this[kWriteToOutput](this[kPrompt]+
+(this[kColorize]?.(lines[0])??lines[0]));
 
 // For continuation lines, add the "|" prefix
 for(leti=1;i<lines.length;i++){
-this[kWriteToOutput](`\n${kMultilinePrompt.description}`+lines[i]);
+this[kWriteToOutput](`\n${kMultilinePrompt.description}`+
+(this[kColorize]?.(lines[i])??lines[i]));
 }
 }else{
 // Write the prompt and the current buffer content.
-this[kWriteToOutput](line);
+this[kWriteToOutput](this[kPrompt]+
+(this[kColorize]?.(this.line)??this.line));
 }
 
 // Force terminal to allocate a new line
@@ -687,7 +693,11 @@ class Interface extends InterfaceConstructor {
 this.line+=c;
 }
 this.cursor+=c.length;
-this[kWriteToOutput](c);
+if(this[kColorize]===undefined){
+this[kWriteToOutput](c);
+}else{
+this[kRefreshLine]();
+}
 return;
 }
 if(this.cursor<this.line.length){
@@ -706,7 +716,7 @@ class Interface extends InterfaceConstructor {
 this.cursor+=c.length;
 constnewPos=this.getCursorPos();
 
-if(oldPos.rows<newPos.rows){
+if(oldPos.rows<newPos.rows||this[kColorize]!==undefined){
 this[kRefreshLine]();
 }else{
 this[kWriteToOutput](c);

lib/internal/repl/highlight.js

@@ -0,0 +1,89 @@
+'use strict';
+
+const{
+ FunctionPrototypeBind,
+ StringPrototypeSlice,
+}=primordials;
+
+const{ stylizeWithColor }=require('internal/util/inspect');
+const{ Parser }=require('internal/deps/acorn/acorn/dist/acorn');
+
+consttokenizer=FunctionPrototypeBind(Parser.tokenizer,Parser);
+
+functiontokenStyle(token){
+const{ label, keyword }=token.type;
+
+if(keyword!==undefined){
+if(label==='true'||label==='false')return'boolean';
+if(label==='null')return'null';
+if(label==='import'||label==='export')return'module';
+return'special';
+}
+
+switch(label){
+case'name':
+switch(token.value){
+case'undefined':
+return'undefined';
+case'NaN':
+case'Infinity':
+return'number';
+case'Symbol':
+return'symbol';
+case'Date':
+return'date';
+default:
+returnundefined;
+}
+case'num':
+return'number';
+case'bigint':
+return'bigint';
+case'string':
+case'template':
+case'`':
+return'string';
+case'regexp':
+return'regexp';
+default:
+returnundefined;
+}
+}
+
+functionhighlight(code){
+if(code.length===0)returncode;
+
+letresult='';
+letoffset=0;
+functionwrite(start,end,style){
+result+=
+StringPrototypeSlice(code,offset,start)+
+stylizeWithColor(StringPrototypeSlice(code,start,end),style);
+offset=end;
+}
+
+try{
+constiterator=tokenizer(code,{
+__proto__: null,
+allowHashBang: true,
+ecmaVersion: 'latest',
+onComment(_block,_text,start,end){
+write(start,end,'undefined');
+},
+});
+
+for(consttokenofiterator){
+conststyle=tokenStyle(token);
+if(style!==undefined){
+write(token.start,token.end,style);
+}
+}
+}catch{
+// Acorn throws for unfinished strings, templates, and comments. Tokens and
+// comments reported before that point are still useful while typing.
+}
+
+returnresult+StringPrototypeSlice(code,offset);
+}
+
+module.exports={ highlight };

lib/internal/util/inspect.js

@@ -3057,6 +3057,7 @@ module.exports = {
  identicalSequenceRange,
  inspect,
  inspectDefaultOptions,
+ stylizeWithColor,
  format,
  formatWithOptions,
  getStringWidth,

lib/repl.js

@@ -109,6 +109,7 @@ const {
 }=require('internal/readline/utils');
 const{ Console }=require('console');
 const{ shouldColorize }=require('internal/util/colors');
+const{ highlight }=require('internal/repl/highlight');
 constCJSModule=require('internal/modules/cjs/loader').Module;
 const{ AsyncLocalStorage }=require('async_hooks');
 letdebug=require('internal/util/debuglog').debuglog('repl',(fn)=>{
@@ -326,6 +327,7 @@ class REPLServer extends Interface {
 terminal: options.terminal,
 historySize: options.historySize,
  prompt,
+colorize: options.useColors ? highlight : undefined,
 });
 
 ObjectDefineProperty(this,'inputStream',{

test/parallel/test-repl-highlight.js

@@ -0,0 +1,61 @@
+// Flags: --expose-internals
+'use strict';
+
+constcommon=require('../common');
+constassert=require('assert');
+const{ inspect, stripVTControlCharacters }=require('util');
+constArrayStream=require('../common/arraystream');
+const{ highlight }=require('internal/repl/highlight');
+const{ REPLServer }=require('repl');
+
+common.skipIfInspectorDisabled();
+
+assert.strictEqual(stripVTControlCharacters(highlight(
+'const /* comment */ answer = 42; // comment',
+)),'const /* comment */ answer = 42; // comment');
+
+assert.strictEqual(
+highlight('const value = "text"'),
+`\u001b[${inspect.colors.cyan[0]}mconst\u001b[${inspect.colors.cyan[1]}m value = `+
+`\u001b[${inspect.colors.green[0]}m"text"\u001b[${inspect.colors.green[1]}m`,
+);
+
+for(constsourceof[
+'undefined',
+'NaN',
+'Infinity',
+'Symbol.iterator',
+'Date.now()',
+'true',
+'null',
+'1n',
+'/regexp/u',
+'import("node:fs")',
+]){
+assert.notStrictEqual(highlight(source),source);
+}
+
+// Incomplete source is expected while the user is typing.
+highlight('const value = "');
+
+{
+constinput=newArrayStream();
+constoutput=newArrayStream();
+letrendered='';
+output.write=(chunk)=>{
+rendered+=chunk;
+};
+
+constrepl=newREPLServer({
+ input,
+ output,
+prompt: '',
+terminal: true,
+useColors: false,
+});
+rendered='';
+repl.write('const');
+
+assert.strictEqual(rendered,'const');
+repl.close();
+}

test/parallel/test-repl-multiline.js

@@ -2,23 +2,24 @@
 constcommon=require('../common');
 constassert=require('assert');
 const{ startNewREPLServer }=require('../common/repl');
+const{ stripVTControlCharacters }=require('util');
 
 constinput=['const foo = {','};','foo'];
 
 functionrun({ useColors }){
 const{ replServer, output }=startNewREPLServer({ useColors });
 
 replServer.on('exit',common.mustCall(()=>{
-constactual=output.accumulator.split('\n');
+// The output contains various escape codes, including
+// screen clears and others, so we trim them all to
+// simplify this test.
+constactual=stripVTControlCharacters(output.accumulator);
 
-// Validate the output, which contains terminal escape codes.
-assert.strictEqual(actual.length,6);
-assert.ok(actual[0].endsWith(input[0]));
-assert.ok(actual[1].includes('| '));
-assert.ok(actual[1].endsWith(input[1]));
-assert.ok(actual[2].includes('undefined'));
-assert.ok(actual[3].endsWith(input[2]));
-assert.strictEqual(actual[4],'{}');
+constfirstStatementIdx=actual.indexOf(input.slice(0,1).join('\n| '));
+assert(firstStatementIdx>-1);
+
+assert(actual.slice(firstStatementIdx).includes('undefined'));
+assert(actual.slice(firstStatementIdx).includes('foo'));
 }));
 
 input.forEach((line)=>replServer.write(`${line}\n`));

test/parallel/test-repl-preview-newlines.js

@@ -6,7 +6,14 @@ const { startNewREPLServer } = require('../common/repl');
 
 common.skipIfInspectorDisabled();
 
-const{ input, output }=startNewREPLServer({useColors: true});
+// Ignore terminal settings so the preview remains active under TERM=dumb.
+process.env.TERM='';
+
+// Keep syntax highlighting out of this test so it only covers preview layout.
+// Preview and result colors are enabled after readline is initialized.
+const{ input, output, replServer }=startNewREPLServer({useColors: false});
+replServer.useColors=true;
+replServer.writer.options.colors=true;
 
 output.accumulator='';
 

test/parallel/test-repl-preview-without-inspector.js

@@ -69,9 +69,13 @@ const repl = new REPLServer({
 prompt: PROMPT,
 stream: newREPLStream(),
 ignoreUndefined: true,
-useColors: true,
+// Keep syntax highlighting out of these preview transcript assertions.
+// Preview and result colors are enabled after readline is initialized.
+useColors: false,
 terminal: true,
 });
+repl.useColors=true;
+repl.writer.options.colors=true;
 
 repl.inputStream.run([
 'function foo(x) { return x; }',

test/parallel/test-repl-preview.js

@@ -61,9 +61,13 @@ async function tests(options) {
 prompt: PROMPT,
 stream: newREPLStream(),
 ignoreUndefined: true,
-useColors: true,
+// Keep syntax highlighting out of these preview transcript assertions.
+// Preview and result colors are enabled after readline is initialized.
+useColors: false,
  ...options
 });
+repl.useColors=true;
+repl.writer.options.colors=true;
 
 repl.inputStream.run([
 'function foo(x) { return x; }',

test/parallel/test-repl-reverse-search.js

@@ -329,7 +329,9 @@ function runTest() {
 }),
 completer: opts.completer,
  prompt,
-useColors: opts.useColors||false,
+// Keep syntax highlighting out of the reverse-search transcript. Result
+// colors are enabled below after readline has been initialized.
+useColors: false,
 terminal: true
 },common.mustCall((err,repl)=>{
 if(err){
@@ -351,6 +353,11 @@ function runTest() {
 setImmediate(runTestWrap,true);
 }));
 
+if(opts.useColors){
+repl.useColors=true;
+repl.writer.options.colors=true;
+}
+
 if(opts.columns){
 Object.defineProperty(repl,'columns',{
 value: opts.columns,

lib/internal/readline/interface.js

@@ -157,13 +157,15 @@ const kPreviousCursorCols = Symbol('_previousCursorCols');
 constkMultilineMove=Symbol('_multilineMove');
 constkPreviousPrevRows=Symbol('_previousPrevRows');
 constkAddNewLineOnTTY=Symbol('_addNewLineOnTTY');
+constkColorize=Symbol('_colorize');
 
 functionInterfaceConstructor(input,output,completer,terminal){
 this[kSawReturnAt]=0;
 // TODO(BridgeAR): Document this property. The name is not ideal, so we
 // might want to expose an alias and document that instead.
 this.isCompletionEnabled=true;
 this[kSawKeyPress]=false;
+this[kColorize]=undefined;
 this[kPreviousKey]=null;
 this.escapeCodeTimeout=ESCAPE_CODE_TIMEOUT;
 this.tabSize=8;
@@ -186,6 +188,7 @@ function InterfaceConstructor(input, output, completer, terminal) {
 consthistorySize=input.historySize;
 consthistory=input.history;
 constremoveHistoryDuplicates=input.removeHistoryDuplicates;
+this[kColorize]=input.colorize;
 
 if(input.tabSize!==undefined){
 validateUint32(input.tabSize,'tabSize',true);
@@ -523,15 +526,18 @@ class Interface extends InterfaceConstructor {
 if(this[kIsMultiline]){
 constlines=StringPrototypeSplit(this.line,'\n');
 // Write first line with normal prompt
-this[kWriteToOutput](this[kPrompt]+lines[0]);
+this[kWriteToOutput](this[kPrompt]+
+(this[kColorize]?.(lines[0])??lines[0]));
 
 // For continuation lines, add the "|" prefix
 for(leti=1;i<lines.length;i++){
-this[kWriteToOutput](`\n${kMultilinePrompt.description}`+lines[i]);
+this[kWriteToOutput](`\n${kMultilinePrompt.description}`+
+(this[kColorize]?.(lines[i])??lines[i]));
 }
 }else{
 // Write the prompt and the current buffer content.
-this[kWriteToOutput](line);
+this[kWriteToOutput](this[kPrompt]+
+(this[kColorize]?.(this.line)??this.line));
 }
 
 // Force terminal to allocate a new line
@@ -687,7 +693,11 @@ class Interface extends InterfaceConstructor {
 this.line+=c;
 }
 this.cursor+=c.length;
-this[kWriteToOutput](c);
+if(this[kColorize]===undefined){
+this[kWriteToOutput](c);
+}else{
+this[kRefreshLine]();
+}
 return;
 }
 if(this.cursor<this.line.length){
@@ -706,7 +716,7 @@ class Interface extends InterfaceConstructor {
 this.cursor+=c.length;
 constnewPos=this.getCursorPos();
 
-if(oldPos.rows<newPos.rows){
+if(oldPos.rows<newPos.rows||this[kColorize]!==undefined){
 this[kRefreshLine]();
 }else{
 this[kWriteToOutput](c);

lib/internal/repl/highlight.js

@@ -0,0 +1,89 @@
+'use strict';
+
+const{
+ FunctionPrototypeBind,
+ StringPrototypeSlice,
+}=primordials;
+
+const{ stylizeWithColor }=require('internal/util/inspect');
+const{ Parser }=require('internal/deps/acorn/acorn/dist/acorn');
+
+consttokenizer=FunctionPrototypeBind(Parser.tokenizer,Parser);
+
+functiontokenStyle(token){
+const{ label, keyword }=token.type;
+
+if(keyword!==undefined){
+if(label==='true'||label==='false')return'boolean';
+if(label==='null')return'null';
+if(label==='import'||label==='export')return'module';
+return'special';
+}
+
+switch(label){
+case'name':
+switch(token.value){
+case'undefined':
+return'undefined';
+case'NaN':
+case'Infinity':
+return'number';
+case'Symbol':
+return'symbol';
+case'Date':
+return'date';
+default:
+returnundefined;
+}
+case'num':
+return'number';
+case'bigint':
+return'bigint';
+case'string':
+case'template':
+case'`':
+return'string';
+case'regexp':
+return'regexp';
+default:
+returnundefined;
+}
+}
+
+functionhighlight(code){
+if(code.length===0)returncode;
+
+letresult='';
+letoffset=0;
+functionwrite(start,end,style){
+result+=
+StringPrototypeSlice(code,offset,start)+
+stylizeWithColor(StringPrototypeSlice(code,start,end),style);
+offset=end;
+}
+
+try{
+constiterator=tokenizer(code,{
+__proto__: null,
+allowHashBang: true,
+ecmaVersion: 'latest',
+onComment(_block,_text,start,end){
+write(start,end,'undefined');
+},
+});
+
+for(consttokenofiterator){
+conststyle=tokenStyle(token);
+if(style!==undefined){
+write(token.start,token.end,style);
+}
+}
+}catch{
+// Acorn throws for unfinished strings, templates, and comments. Tokens and
+// comments reported before that point are still useful while typing.
+}
+
+returnresult+StringPrototypeSlice(code,offset);
+}
+
+module.exports={ highlight };

lib/internal/util/inspect.js

@@ -3057,6 +3057,7 @@ module.exports = {
  identicalSequenceRange,
  inspect,
  inspectDefaultOptions,
+ stylizeWithColor,
  format,
  formatWithOptions,
  getStringWidth,

lib/repl.js

@@ -109,6 +109,7 @@ const {
 }=require('internal/readline/utils');
 const{ Console }=require('console');
 const{ shouldColorize }=require('internal/util/colors');
+const{ highlight }=require('internal/repl/highlight');
 constCJSModule=require('internal/modules/cjs/loader').Module;
 const{ AsyncLocalStorage }=require('async_hooks');
 letdebug=require('internal/util/debuglog').debuglog('repl',(fn)=>{
@@ -326,6 +327,7 @@ class REPLServer extends Interface {
 terminal: options.terminal,
 historySize: options.historySize,
  prompt,
+colorize: options.useColors ? highlight : undefined,
 });
 
 ObjectDefineProperty(this,'inputStream',{

test/parallel/test-repl-highlight.js

@@ -0,0 +1,61 @@
+// Flags: --expose-internals
+'use strict';
+
+constcommon=require('../common');
+constassert=require('assert');
+const{ inspect, stripVTControlCharacters }=require('util');
+constArrayStream=require('../common/arraystream');
+const{ highlight }=require('internal/repl/highlight');
+const{ REPLServer }=require('repl');
+
+common.skipIfInspectorDisabled();
+
+assert.strictEqual(stripVTControlCharacters(highlight(
+'const /* comment */ answer = 42; // comment',
+)),'const /* comment */ answer = 42; // comment');
+
+assert.strictEqual(
+highlight('const value = "text"'),
+`\u001b[${inspect.colors.cyan[0]}mconst\u001b[${inspect.colors.cyan[1]}m value = `+
+`\u001b[${inspect.colors.green[0]}m"text"\u001b[${inspect.colors.green[1]}m`,
+);
+
+for(constsourceof[
+'undefined',
+'NaN',
+'Infinity',
+'Symbol.iterator',
+'Date.now()',
+'true',
+'null',
+'1n',
+'/regexp/u',
+'import("node:fs")',
+]){
+assert.notStrictEqual(highlight(source),source);
+}
+
+// Incomplete source is expected while the user is typing.
+highlight('const value = "');
+
+{
+constinput=newArrayStream();
+constoutput=newArrayStream();
+letrendered='';
+output.write=(chunk)=>{
+rendered+=chunk;
+};
+
+constrepl=newREPLServer({
+ input,
+ output,
+prompt: '',
+terminal: true,
+useColors: false,
+});
+rendered='';
+repl.write('const');
+
+assert.strictEqual(rendered,'const');
+repl.close();
+}

test/parallel/test-repl-multiline.js

@@ -2,23 +2,24 @@
 constcommon=require('../common');
 constassert=require('assert');
 const{ startNewREPLServer }=require('../common/repl');
+const{ stripVTControlCharacters }=require('util');
 
 constinput=['const foo = {','};','foo'];
 
 functionrun({ useColors }){
 const{ replServer, output }=startNewREPLServer({ useColors });
 
 replServer.on('exit',common.mustCall(()=>{
-constactual=output.accumulator.split('\n');
+// The output contains various escape codes, including
+// screen clears and others, so we trim them all to
+// simplify this test.
+constactual=stripVTControlCharacters(output.accumulator);
 
-// Validate the output, which contains terminal escape codes.
-assert.strictEqual(actual.length,6);
-assert.ok(actual[0].endsWith(input[0]));
-assert.ok(actual[1].includes('| '));
-assert.ok(actual[1].endsWith(input[1]));
-assert.ok(actual[2].includes('undefined'));
-assert.ok(actual[3].endsWith(input[2]));
-assert.strictEqual(actual[4],'{}');
+constfirstStatementIdx=actual.indexOf(input.slice(0,1).join('\n| '));
+assert(firstStatementIdx>-1);
+
+assert(actual.slice(firstStatementIdx).includes('undefined'));
+assert(actual.slice(firstStatementIdx).includes('foo'));
 }));
 
 input.forEach((line)=>replServer.write(`${line}\n`));

test/parallel/test-repl-preview-newlines.js

@@ -6,7 +6,14 @@ const { startNewREPLServer } = require('../common/repl');
 
 common.skipIfInspectorDisabled();
 
-const{ input, output }=startNewREPLServer({useColors: true});
+// Ignore terminal settings so the preview remains active under TERM=dumb.
+process.env.TERM='';
+
+// Keep syntax highlighting out of this test so it only covers preview layout.
+// Preview and result colors are enabled after readline is initialized.
+const{ input, output, replServer }=startNewREPLServer({useColors: false});
+replServer.useColors=true;
+replServer.writer.options.colors=true;
 
 output.accumulator='';
 

test/parallel/test-repl-preview-without-inspector.js

@@ -69,9 +69,13 @@ const repl = new REPLServer({
 prompt: PROMPT,
 stream: newREPLStream(),
 ignoreUndefined: true,
-useColors: true,
+// Keep syntax highlighting out of these preview transcript assertions.
+// Preview and result colors are enabled after readline is initialized.
+useColors: false,
 terminal: true,
 });
+repl.useColors=true;
+repl.writer.options.colors=true;
 
 repl.inputStream.run([
 'function foo(x) { return x; }',

test/parallel/test-repl-preview.js

@@ -61,9 +61,13 @@ async function tests(options) {
 prompt: PROMPT,
 stream: newREPLStream(),
 ignoreUndefined: true,
-useColors: true,
+// Keep syntax highlighting out of these preview transcript assertions.
+// Preview and result colors are enabled after readline is initialized.
+useColors: false,
  ...options
 });
+repl.useColors=true;
+repl.writer.options.colors=true;
 
 repl.inputStream.run([
 'function foo(x) { return x; }',

test/parallel/test-repl-reverse-search.js

@@ -329,7 +329,9 @@ function runTest() {
 }),
 completer: opts.completer,
  prompt,
-useColors: opts.useColors||false,
+// Keep syntax highlighting out of the reverse-search transcript. Result
+// colors are enabled below after readline has been initialized.
+useColors: false,
 terminal: true
 },common.mustCall((err,repl)=>{
 if(err){
@@ -351,6 +353,11 @@ function runTest() {
 setImmediate(runTestWrap,true);
 }));
 
+if(opts.useColors){
+repl.useColors=true;
+repl.writer.options.colors=true;
+}
+
 if(opts.columns){
 Object.defineProperty(repl,'columns',{
 value: opts.columns,

lib/internal/readline/interface.js

@@ -157,13 +157,15 @@ const kPreviousCursorCols = Symbol('_previousCursorCols');
 constkMultilineMove=Symbol('_multilineMove');
 constkPreviousPrevRows=Symbol('_previousPrevRows');
 constkAddNewLineOnTTY=Symbol('_addNewLineOnTTY');
+constkColorize=Symbol('_colorize');
 
 functionInterfaceConstructor(input,output,completer,terminal){
 this[kSawReturnAt]=0;
 // TODO(BridgeAR): Document this property. The name is not ideal, so we
 // might want to expose an alias and document that instead.
 this.isCompletionEnabled=true;
 this[kSawKeyPress]=false;
+this[kColorize]=undefined;
 this[kPreviousKey]=null;
 this.escapeCodeTimeout=ESCAPE_CODE_TIMEOUT;
 this.tabSize=8;
@@ -186,6 +188,7 @@ function InterfaceConstructor(input, output, completer, terminal) {
 consthistorySize=input.historySize;
 consthistory=input.history;
 constremoveHistoryDuplicates=input.removeHistoryDuplicates;
+this[kColorize]=input.colorize;
 
 if(input.tabSize!==undefined){
 validateUint32(input.tabSize,'tabSize',true);
@@ -523,15 +526,18 @@ class Interface extends InterfaceConstructor {
 if(this[kIsMultiline]){
 constlines=StringPrototypeSplit(this.line,'\n');
 // Write first line with normal prompt
-this[kWriteToOutput](this[kPrompt]+lines[0]);
+this[kWriteToOutput](this[kPrompt]+
+(this[kColorize]?.(lines[0])??lines[0]));
 
 // For continuation lines, add the "|" prefix
 for(leti=1;i<lines.length;i++){
-this[kWriteToOutput](`\n${kMultilinePrompt.description}`+lines[i]);
+this[kWriteToOutput](`\n${kMultilinePrompt.description}`+
+(this[kColorize]?.(lines[i])??lines[i]));
 }
 }else{
 // Write the prompt and the current buffer content.
-this[kWriteToOutput](line);
+this[kWriteToOutput](this[kPrompt]+
+(this[kColorize]?.(this.line)??this.line));
 }
 
 // Force terminal to allocate a new line
@@ -687,7 +693,11 @@ class Interface extends InterfaceConstructor {
 this.line+=c;
 }
 this.cursor+=c.length;
-this[kWriteToOutput](c);
+if(this[kColorize]===undefined){
+this[kWriteToOutput](c);
+}else{
+this[kRefreshLine]();
+}
 return;
 }
 if(this.cursor<this.line.length){
@@ -706,7 +716,7 @@ class Interface extends InterfaceConstructor {
 this.cursor+=c.length;
 constnewPos=this.getCursorPos();
 
-if(oldPos.rows<newPos.rows){
+if(oldPos.rows<newPos.rows||this[kColorize]!==undefined){
 this[kRefreshLine]();
 }else{
 this[kWriteToOutput](c);

lib/internal/repl/highlight.js

@@ -0,0 +1,89 @@
+'use strict';
+
+const{
+ FunctionPrototypeBind,
+ StringPrototypeSlice,
+}=primordials;
+
+const{ stylizeWithColor }=require('internal/util/inspect');
+const{ Parser }=require('internal/deps/acorn/acorn/dist/acorn');
+
+consttokenizer=FunctionPrototypeBind(Parser.tokenizer,Parser);
+
+functiontokenStyle(token){
+const{ label, keyword }=token.type;
+
+if(keyword!==undefined){
+if(label==='true'||label==='false')return'boolean';
+if(label==='null')return'null';
+if(label==='import'||label==='export')return'module';
+return'special';
+}
+
+switch(label){
+case'name':
+switch(token.value){
+case'undefined':
+return'undefined';
+case'NaN':
+case'Infinity':
+return'number';
+case'Symbol':
+return'symbol';
+case'Date':
+return'date';
+default:
+returnundefined;
+}
+case'num':
+return'number';
+case'bigint':
+return'bigint';
+case'string':
+case'template':
+case'`':
+return'string';
+case'regexp':
+return'regexp';
+default:
+returnundefined;
+}
+}
+
+functionhighlight(code){
+if(code.length===0)returncode;
+
+letresult='';
+letoffset=0;
+functionwrite(start,end,style){
+result+=
+StringPrototypeSlice(code,offset,start)+
+stylizeWithColor(StringPrototypeSlice(code,start,end),style);
+offset=end;
+}
+
+try{
+constiterator=tokenizer(code,{
+__proto__: null,
+allowHashBang: true,
+ecmaVersion: 'latest',
+onComment(_block,_text,start,end){
+write(start,end,'undefined');
+},
+});
+
+for(consttokenofiterator){
+conststyle=tokenStyle(token);
+if(style!==undefined){
+write(token.start,token.end,style);
+}
+}
+}catch{
+// Acorn throws for unfinished strings, templates, and comments. Tokens and
+// comments reported before that point are still useful while typing.
+}
+
+returnresult+StringPrototypeSlice(code,offset);
+}
+
+module.exports={ highlight };

lib/internal/util/inspect.js

@@ -3057,6 +3057,7 @@ module.exports = {
  identicalSequenceRange,
  inspect,
  inspectDefaultOptions,
+ stylizeWithColor,
  format,
  formatWithOptions,
  getStringWidth,

lib/repl.js

@@ -109,6 +109,7 @@ const {
 }=require('internal/readline/utils');
 const{ Console }=require('console');
 const{ shouldColorize }=require('internal/util/colors');
+const{ highlight }=require('internal/repl/highlight');
 constCJSModule=require('internal/modules/cjs/loader').Module;
 const{ AsyncLocalStorage }=require('async_hooks');
 letdebug=require('internal/util/debuglog').debuglog('repl',(fn)=>{
@@ -326,6 +327,7 @@ class REPLServer extends Interface {
 terminal: options.terminal,
 historySize: options.historySize,
  prompt,
+colorize: options.useColors ? highlight : undefined,
 });
 
 ObjectDefineProperty(this,'inputStream',{

test/parallel/test-repl-highlight.js

@@ -0,0 +1,61 @@
+// Flags: --expose-internals
+'use strict';
+
+constcommon=require('../common');
+constassert=require('assert');
+const{ inspect, stripVTControlCharacters }=require('util');
+constArrayStream=require('../common/arraystream');
+const{ highlight }=require('internal/repl/highlight');
+const{ REPLServer }=require('repl');
+
+common.skipIfInspectorDisabled();
+
+assert.strictEqual(stripVTControlCharacters(highlight(
+'const /* comment */ answer = 42; // comment',
+)),'const /* comment */ answer = 42; // comment');
+
+assert.strictEqual(
+highlight('const value = "text"'),
+`\u001b[${inspect.colors.cyan[0]}mconst\u001b[${inspect.colors.cyan[1]}m value = `+
+`\u001b[${inspect.colors.green[0]}m"text"\u001b[${inspect.colors.green[1]}m`,
+);
+
+for(constsourceof[
+'undefined',
+'NaN',
+'Infinity',
+'Symbol.iterator',
+'Date.now()',
+'true',
+'null',
+'1n',
+'/regexp/u',
+'import("node:fs")',
+]){
+assert.notStrictEqual(highlight(source),source);
+}
+
+// Incomplete source is expected while the user is typing.
+highlight('const value = "');
+
+{
+constinput=newArrayStream();
+constoutput=newArrayStream();
+letrendered='';
+output.write=(chunk)=>{
+rendered+=chunk;
+};
+
+constrepl=newREPLServer({
+ input,
+ output,
+prompt: '',
+terminal: true,
+useColors: false,
+});
+rendered='';
+repl.write('const');
+
+assert.strictEqual(rendered,'const');
+repl.close();
+}

test/parallel/test-repl-multiline.js

@@ -2,23 +2,24 @@
 constcommon=require('../common');
 constassert=require('assert');
 const{ startNewREPLServer }=require('../common/repl');
+const{ stripVTControlCharacters }=require('util');
 
 constinput=['const foo = {','};','foo'];
 
 functionrun({ useColors }){
 const{ replServer, output }=startNewREPLServer({ useColors });
 
 replServer.on('exit',common.mustCall(()=>{
-constactual=output.accumulator.split('\n');
+// The output contains various escape codes, including
+// screen clears and others, so we trim them all to
+// simplify this test.
+constactual=stripVTControlCharacters(output.accumulator);
 
-// Validate the output, which contains terminal escape codes.
-assert.strictEqual(actual.length,6);
-assert.ok(actual[0].endsWith(input[0]));
-assert.ok(actual[1].includes('| '));
-assert.ok(actual[1].endsWith(input[1]));
-assert.ok(actual[2].includes('undefined'));
-assert.ok(actual[3].endsWith(input[2]));
-assert.strictEqual(actual[4],'{}');
+constfirstStatementIdx=actual.indexOf(input.slice(0,1).join('\n| '));
+assert(firstStatementIdx>-1);
+
+assert(actual.slice(firstStatementIdx).includes('undefined'));
+assert(actual.slice(firstStatementIdx).includes('foo'));
 }));
 
 input.forEach((line)=>replServer.write(`${line}\n`));

test/parallel/test-repl-preview-newlines.js

@@ -6,7 +6,14 @@ const { startNewREPLServer } = require('../common/repl');
 
 common.skipIfInspectorDisabled();
 
-const{ input, output }=startNewREPLServer({useColors: true});
+// Ignore terminal settings so the preview remains active under TERM=dumb.
+process.env.TERM='';
+
+// Keep syntax highlighting out of this test so it only covers preview layout.
+// Preview and result colors are enabled after readline is initialized.
+const{ input, output, replServer }=startNewREPLServer({useColors: false});
+replServer.useColors=true;
+replServer.writer.options.colors=true;
 
 output.accumulator='';
 

test/parallel/test-repl-preview-without-inspector.js

@@ -69,9 +69,13 @@ const repl = new REPLServer({
 prompt: PROMPT,
 stream: newREPLStream(),
 ignoreUndefined: true,
-useColors: true,
+// Keep syntax highlighting out of these preview transcript assertions.
+// Preview and result colors are enabled after readline is initialized.
+useColors: false,
 terminal: true,
 });
+repl.useColors=true;
+repl.writer.options.colors=true;
 
 repl.inputStream.run([
 'function foo(x) { return x; }',

test/parallel/test-repl-preview.js

@@ -61,9 +61,13 @@ async function tests(options) {
 prompt: PROMPT,
 stream: newREPLStream(),
 ignoreUndefined: true,
-useColors: true,
+// Keep syntax highlighting out of these preview transcript assertions.
+// Preview and result colors are enabled after readline is initialized.
+useColors: false,
  ...options
 });
+repl.useColors=true;
+repl.writer.options.colors=true;
 
 repl.inputStream.run([
 'function foo(x) { return x; }',

test/parallel/test-repl-reverse-search.js

@@ -329,7 +329,9 @@ function runTest() {
 }),
 completer: opts.completer,
  prompt,
-useColors: opts.useColors||false,
+// Keep syntax highlighting out of the reverse-search transcript. Result
+// colors are enabled below after readline has been initialized.
+useColors: false,
 terminal: true
 },common.mustCall((err,repl)=>{
 if(err){
@@ -351,6 +353,11 @@ function runTest() {
 setImmediate(runTestWrap,true);
 }));
 
+if(opts.useColors){
+repl.useColors=true;
+repl.writer.options.colors=true;
+}
+
 if(opts.columns){
 Object.defineProperty(repl,'columns',{
 value: opts.columns,

lib/internal/readline/interface.js

@@ -157,13 +157,15 @@ const kPreviousCursorCols = Symbol('_previousCursorCols');
 constkMultilineMove=Symbol('_multilineMove');
 constkPreviousPrevRows=Symbol('_previousPrevRows');
 constkAddNewLineOnTTY=Symbol('_addNewLineOnTTY');
+constkColorize=Symbol('_colorize');
 
 functionInterfaceConstructor(input,output,completer,terminal){
 this[kSawReturnAt]=0;
 // TODO(BridgeAR): Document this property. The name is not ideal, so we
 // might want to expose an alias and document that instead.
 this.isCompletionEnabled=true;
 this[kSawKeyPress]=false;
+this[kColorize]=undefined;
 this[kPreviousKey]=null;
 this.escapeCodeTimeout=ESCAPE_CODE_TIMEOUT;
 this.tabSize=8;
@@ -186,6 +188,7 @@ function InterfaceConstructor(input, output, completer, terminal) {
 consthistorySize=input.historySize;
 consthistory=input.history;
 constremoveHistoryDuplicates=input.removeHistoryDuplicates;
+this[kColorize]=input.colorize;
 
 if(input.tabSize!==undefined){
 validateUint32(input.tabSize,'tabSize',true);
@@ -523,15 +526,18 @@ class Interface extends InterfaceConstructor {
 if(this[kIsMultiline]){
 constlines=StringPrototypeSplit(this.line,'\n');
 // Write first line with normal prompt
-this[kWriteToOutput](this[kPrompt]+lines[0]);
+this[kWriteToOutput](this[kPrompt]+
+(this[kColorize]?.(lines[0])??lines[0]));
 
 // For continuation lines, add the "|" prefix
 for(leti=1;i<lines.length;i++){
-this[kWriteToOutput](`\n${kMultilinePrompt.description}`+lines[i]);
+this[kWriteToOutput](`\n${kMultilinePrompt.description}`+
+(this[kColorize]?.(lines[i])??lines[i]));
 }
 }else{
 // Write the prompt and the current buffer content.
-this[kWriteToOutput](line);
+this[kWriteToOutput](this[kPrompt]+
+(this[kColorize]?.(this.line)??this.line));
 }
 
 // Force terminal to allocate a new line
@@ -687,7 +693,11 @@ class Interface extends InterfaceConstructor {
 this.line+=c;
 }
 this.cursor+=c.length;
-this[kWriteToOutput](c);
+if(this[kColorize]===undefined){
+this[kWriteToOutput](c);
+}else{
+this[kRefreshLine]();
+}
 return;
 }
 if(this.cursor<this.line.length){
@@ -706,7 +716,7 @@ class Interface extends InterfaceConstructor {
 this.cursor+=c.length;
 constnewPos=this.getCursorPos();
 
-if(oldPos.rows<newPos.rows){
+if(oldPos.rows<newPos.rows||this[kColorize]!==undefined){
 this[kRefreshLine]();
 }else{
 this[kWriteToOutput](c);

lib/internal/repl/highlight.js

@@ -0,0 +1,89 @@
+'use strict';
+
+const{
+ FunctionPrototypeBind,
+ StringPrototypeSlice,
+}=primordials;
+
+const{ stylizeWithColor }=require('internal/util/inspect');
+const{ Parser }=require('internal/deps/acorn/acorn/dist/acorn');
+
+consttokenizer=FunctionPrototypeBind(Parser.tokenizer,Parser);
+
+functiontokenStyle(token){
+const{ label, keyword }=token.type;
+
+if(keyword!==undefined){
+if(label==='true'||label==='false')return'boolean';
+if(label==='null')return'null';
+if(label==='import'||label==='export')return'module';
+return'special';
+}
+
+switch(label){
+case'name':
+switch(token.value){
+case'undefined':
+return'undefined';
+case'NaN':
+case'Infinity':
+return'number';
+case'Symbol':
+return'symbol';
+case'Date':
+return'date';
+default:
+returnundefined;
+}
+case'num':
+return'number';
+case'bigint':
+return'bigint';
+case'string':
+case'template':
+case'`':
+return'string';
+case'regexp':
+return'regexp';
+default:
+returnundefined;
+}
+}
+
+functionhighlight(code){
+if(code.length===0)returncode;
+
+letresult='';
+letoffset=0;
+functionwrite(start,end,style){
+result+=
+StringPrototypeSlice(code,offset,start)+
+stylizeWithColor(StringPrototypeSlice(code,start,end),style);
+offset=end;
+}
+
+try{
+constiterator=tokenizer(code,{
+__proto__: null,
+allowHashBang: true,
+ecmaVersion: 'latest',
+onComment(_block,_text,start,end){
+write(start,end,'undefined');
+},
+});
+
+for(consttokenofiterator){
+conststyle=tokenStyle(token);
+if(style!==undefined){
+write(token.start,token.end,style);
+}
+}
+}catch{
+// Acorn throws for unfinished strings, templates, and comments. Tokens and
+// comments reported before that point are still useful while typing.
+}
+
+returnresult+StringPrototypeSlice(code,offset);
+}
+
+module.exports={ highlight };

lib/internal/util/inspect.js

@@ -3057,6 +3057,7 @@ module.exports = {
  identicalSequenceRange,
  inspect,
  inspectDefaultOptions,
+ stylizeWithColor,
  format,
  formatWithOptions,
  getStringWidth,

lib/repl.js

@@ -109,6 +109,7 @@ const {
 }=require('internal/readline/utils');
 const{ Console }=require('console');
 const{ shouldColorize }=require('internal/util/colors');
+const{ highlight }=require('internal/repl/highlight');
 constCJSModule=require('internal/modules/cjs/loader').Module;
 const{ AsyncLocalStorage }=require('async_hooks');
 letdebug=require('internal/util/debuglog').debuglog('repl',(fn)=>{
@@ -326,6 +327,7 @@ class REPLServer extends Interface {
 terminal: options.terminal,
 historySize: options.historySize,
  prompt,
+colorize: options.useColors ? highlight : undefined,
 });
 
 ObjectDefineProperty(this,'inputStream',{

test/parallel/test-repl-highlight.js

@@ -0,0 +1,61 @@
+// Flags: --expose-internals
+'use strict';
+
+constcommon=require('../common');
+constassert=require('assert');
+const{ inspect, stripVTControlCharacters }=require('util');
+constArrayStream=require('../common/arraystream');
+const{ highlight }=require('internal/repl/highlight');
+const{ REPLServer }=require('repl');
+
+common.skipIfInspectorDisabled();
+
+assert.strictEqual(stripVTControlCharacters(highlight(
+'const /* comment */ answer = 42; // comment',
+)),'const /* comment */ answer = 42; // comment');
+
+assert.strictEqual(
+highlight('const value = "text"'),
+`\u001b[${inspect.colors.cyan[0]}mconst\u001b[${inspect.colors.cyan[1]}m value = `+
+`\u001b[${inspect.colors.green[0]}m"text"\u001b[${inspect.colors.green[1]}m`,
+);
+
+for(constsourceof[
+'undefined',
+'NaN',
+'Infinity',
+'Symbol.iterator',
+'Date.now()',
+'true',
+'null',
+'1n',
+'/regexp/u',
+'import("node:fs")',
+]){
+assert.notStrictEqual(highlight(source),source);
+}
+
+// Incomplete source is expected while the user is typing.
+highlight('const value = "');
+
+{
+constinput=newArrayStream();
+constoutput=newArrayStream();
+letrendered='';
+output.write=(chunk)=>{
+rendered+=chunk;
+};
+
+constrepl=newREPLServer({
+ input,
+ output,
+prompt: '',
+terminal: true,
+useColors: false,
+});
+rendered='';
+repl.write('const');
+
+assert.strictEqual(rendered,'const');
+repl.close();
+}

test/parallel/test-repl-multiline.js

@@ -2,23 +2,24 @@
 constcommon=require('../common');
 constassert=require('assert');
 const{ startNewREPLServer }=require('../common/repl');
+const{ stripVTControlCharacters }=require('util');
 
 constinput=['const foo = {','};','foo'];
 
 functionrun({ useColors }){
 const{ replServer, output }=startNewREPLServer({ useColors });
 
 replServer.on('exit',common.mustCall(()=>{
-constactual=output.accumulator.split('\n');
+// The output contains various escape codes, including
+// screen clears and others, so we trim them all to
+// simplify this test.
+constactual=stripVTControlCharacters(output.accumulator);
 
-// Validate the output, which contains terminal escape codes.
-assert.strictEqual(actual.length,6);
-assert.ok(actual[0].endsWith(input[0]));
-assert.ok(actual[1].includes('| '));
-assert.ok(actual[1].endsWith(input[1]));
-assert.ok(actual[2].includes('undefined'));
-assert.ok(actual[3].endsWith(input[2]));
-assert.strictEqual(actual[4],'{}');
+constfirstStatementIdx=actual.indexOf(input.slice(0,1).join('\n| '));
+assert(firstStatementIdx>-1);
+
+assert(actual.slice(firstStatementIdx).includes('undefined'));
+assert(actual.slice(firstStatementIdx).includes('foo'));
 }));
 
 input.forEach((line)=>replServer.write(`${line}\n`));

test/parallel/test-repl-preview-newlines.js

@@ -6,7 +6,14 @@ const { startNewREPLServer } = require('../common/repl');
 
 common.skipIfInspectorDisabled();
 
-const{ input, output }=startNewREPLServer({useColors: true});
+// Ignore terminal settings so the preview remains active under TERM=dumb.
+process.env.TERM='';
+
+// Keep syntax highlighting out of this test so it only covers preview layout.
+// Preview and result colors are enabled after readline is initialized.
+const{ input, output, replServer }=startNewREPLServer({useColors: false});
+replServer.useColors=true;
+replServer.writer.options.colors=true;
 
 output.accumulator='';
 

test/parallel/test-repl-preview-without-inspector.js

@@ -69,9 +69,13 @@ const repl = new REPLServer({
 prompt: PROMPT,
 stream: newREPLStream(),
 ignoreUndefined: true,
-useColors: true,
+// Keep syntax highlighting out of these preview transcript assertions.
+// Preview and result colors are enabled after readline is initialized.
+useColors: false,
 terminal: true,
 });
+repl.useColors=true;
+repl.writer.options.colors=true;
 
 repl.inputStream.run([
 'function foo(x) { return x; }',

test/parallel/test-repl-preview.js

@@ -61,9 +61,13 @@ async function tests(options) {
 prompt: PROMPT,
 stream: newREPLStream(),
 ignoreUndefined: true,
-useColors: true,
+// Keep syntax highlighting out of these preview transcript assertions.
+// Preview and result colors are enabled after readline is initialized.
+useColors: false,
  ...options
 });
+repl.useColors=true;
+repl.writer.options.colors=true;
 
 repl.inputStream.run([
 'function foo(x) { return x; }',

test/parallel/test-repl-reverse-search.js

@@ -329,7 +329,9 @@ function runTest() {
 }),
 completer: opts.completer,
  prompt,
-useColors: opts.useColors||false,
+// Keep syntax highlighting out of the reverse-search transcript. Result
+// colors are enabled below after readline has been initialized.
+useColors: false,
 terminal: true
 },common.mustCall((err,repl)=>{
 if(err){
@@ -351,6 +353,11 @@ function runTest() {
 setImmediate(runTestWrap,true);
 }));
 
+if(opts.useColors){
+repl.useColors=true;
+repl.writer.options.colors=true;
+}
+
 if(opts.columns){
 Object.defineProperty(repl,'columns',{
 value: opts.columns,

lib/internal/readline/interface.js

@@ -157,13 +157,15 @@ const kPreviousCursorCols = Symbol('_previousCursorCols');
 constkMultilineMove=Symbol('_multilineMove');
 constkPreviousPrevRows=Symbol('_previousPrevRows');
 constkAddNewLineOnTTY=Symbol('_addNewLineOnTTY');
+constkColorize=Symbol('_colorize');
 
 functionInterfaceConstructor(input,output,completer,terminal){
 this[kSawReturnAt]=0;
 // TODO(BridgeAR): Document this property. The name is not ideal, so we
 // might want to expose an alias and document that instead.
 this.isCompletionEnabled=true;
 this[kSawKeyPress]=false;
+this[kColorize]=undefined;
 this[kPreviousKey]=null;
 this.escapeCodeTimeout=ESCAPE_CODE_TIMEOUT;
 this.tabSize=8;
@@ -186,6 +188,7 @@ function InterfaceConstructor(input, output, completer, terminal) {
 consthistorySize=input.historySize;
 consthistory=input.history;
 constremoveHistoryDuplicates=input.removeHistoryDuplicates;
+this[kColorize]=input.colorize;
 
 if(input.tabSize!==undefined){
 validateUint32(input.tabSize,'tabSize',true);
@@ -523,15 +526,18 @@ class Interface extends InterfaceConstructor {
 if(this[kIsMultiline]){
 constlines=StringPrototypeSplit(this.line,'\n');
 // Write first line with normal prompt
-this[kWriteToOutput](this[kPrompt]+lines[0]);
+this[kWriteToOutput](this[kPrompt]+
+(this[kColorize]?.(lines[0])??lines[0]));
 
 // For continuation lines, add the "|" prefix
 for(leti=1;i<lines.length;i++){
-this[kWriteToOutput](`\n${kMultilinePrompt.description}`+lines[i]);
+this[kWriteToOutput](`\n${kMultilinePrompt.description}`+
+(this[kColorize]?.(lines[i])??lines[i]));
 }
 }else{
 // Write the prompt and the current buffer content.
-this[kWriteToOutput](line);
+this[kWriteToOutput](this[kPrompt]+
+(this[kColorize]?.(this.line)??this.line));
 }
 
 // Force terminal to allocate a new line
@@ -687,7 +693,11 @@ class Interface extends InterfaceConstructor {
 this.line+=c;
 }
 this.cursor+=c.length;
-this[kWriteToOutput](c);
+if(this[kColorize]===undefined){
+this[kWriteToOutput](c);
+}else{
+this[kRefreshLine]();
+}
 return;
 }
 if(this.cursor<this.line.length){
@@ -706,7 +716,7 @@ class Interface extends InterfaceConstructor {
 this.cursor+=c.length;
 constnewPos=this.getCursorPos();
 
-if(oldPos.rows<newPos.rows){
+if(oldPos.rows<newPos.rows||this[kColorize]!==undefined){
 this[kRefreshLine]();
 }else{
 this[kWriteToOutput](c);

lib/internal/repl/highlight.js

@@ -0,0 +1,89 @@
+'use strict';
+
+const{
+ FunctionPrototypeBind,
+ StringPrototypeSlice,
+}=primordials;
+
+const{ stylizeWithColor }=require('internal/util/inspect');
+const{ Parser }=require('internal/deps/acorn/acorn/dist/acorn');
+
+consttokenizer=FunctionPrototypeBind(Parser.tokenizer,Parser);
+
+functiontokenStyle(token){
+const{ label, keyword }=token.type;
+
+if(keyword!==undefined){
+if(label==='true'||label==='false')return'boolean';
+if(label==='null')return'null';
+if(label==='import'||label==='export')return'module';
+return'special';
+}
+
+switch(label){
+case'name':
+switch(token.value){
+case'undefined':
+return'undefined';
+case'NaN':
+case'Infinity':
+return'number';
+case'Symbol':
+return'symbol';
+case'Date':
+return'date';
+default:
+returnundefined;
+}
+case'num':
+return'number';
+case'bigint':
+return'bigint';
+case'string':
+case'template':
+case'`':
+return'string';
+case'regexp':
+return'regexp';
+default:
+returnundefined;
+}
+}
+
+functionhighlight(code){
+if(code.length===0)returncode;
+
+letresult='';
+letoffset=0;
+functionwrite(start,end,style){
+result+=
+StringPrototypeSlice(code,offset,start)+
+stylizeWithColor(StringPrototypeSlice(code,start,end),style);
+offset=end;
+}
+
+try{
+constiterator=tokenizer(code,{
+__proto__: null,
+allowHashBang: true,
+ecmaVersion: 'latest',
+onComment(_block,_text,start,end){
+write(start,end,'undefined');
+},
+});
+
+for(consttokenofiterator){
+conststyle=tokenStyle(token);
+if(style!==undefined){
+write(token.start,token.end,style);
+}
+}
+}catch{
+// Acorn throws for unfinished strings, templates, and comments. Tokens and
+// comments reported before that point are still useful while typing.
+}
+
+returnresult+StringPrototypeSlice(code,offset);
+}
+
+module.exports={ highlight };

lib/internal/util/inspect.js

@@ -3057,6 +3057,7 @@ module.exports = {
  identicalSequenceRange,
  inspect,
  inspectDefaultOptions,
+ stylizeWithColor,
  format,
  formatWithOptions,
  getStringWidth,

lib/repl.js

@@ -109,6 +109,7 @@ const {
 }=require('internal/readline/utils');
 const{ Console }=require('console');
 const{ shouldColorize }=require('internal/util/colors');
+const{ highlight }=require('internal/repl/highlight');
 constCJSModule=require('internal/modules/cjs/loader').Module;
 const{ AsyncLocalStorage }=require('async_hooks');
 letdebug=require('internal/util/debuglog').debuglog('repl',(fn)=>{
@@ -326,6 +327,7 @@ class REPLServer extends Interface {
 terminal: options.terminal,
 historySize: options.historySize,
  prompt,
+colorize: options.useColors ? highlight : undefined,
 });
 
 ObjectDefineProperty(this,'inputStream',{

test/parallel/test-repl-highlight.js

@@ -0,0 +1,61 @@
+// Flags: --expose-internals
+'use strict';
+
+constcommon=require('../common');
+constassert=require('assert');
+const{ inspect, stripVTControlCharacters }=require('util');
+constArrayStream=require('../common/arraystream');
+const{ highlight }=require('internal/repl/highlight');
+const{ REPLServer }=require('repl');
+
+common.skipIfInspectorDisabled();
+
+assert.strictEqual(stripVTControlCharacters(highlight(
+'const /* comment */ answer = 42; // comment',
+)),'const /* comment */ answer = 42; // comment');
+
+assert.strictEqual(
+highlight('const value = "text"'),
+`\u001b[${inspect.colors.cyan[0]}mconst\u001b[${inspect.colors.cyan[1]}m value = `+
+`\u001b[${inspect.colors.green[0]}m"text"\u001b[${inspect.colors.green[1]}m`,
+);
+
+for(constsourceof[
+'undefined',
+'NaN',
+'Infinity',
+'Symbol.iterator',
+'Date.now()',
+'true',
+'null',
+'1n',
+'/regexp/u',
+'import("node:fs")',
+]){
+assert.notStrictEqual(highlight(source),source);
+}
+
+// Incomplete source is expected while the user is typing.
+highlight('const value = "');
+
+{
+constinput=newArrayStream();
+constoutput=newArrayStream();
+letrendered='';
+output.write=(chunk)=>{
+rendered+=chunk;
+};
+
+constrepl=newREPLServer({
+ input,
+ output,
+prompt: '',
+terminal: true,
+useColors: false,
+});
+rendered='';
+repl.write('const');
+
+assert.strictEqual(rendered,'const');
+repl.close();
+}

test/parallel/test-repl-multiline.js

@@ -2,23 +2,24 @@
 constcommon=require('../common');
 constassert=require('assert');
 const{ startNewREPLServer }=require('../common/repl');
+const{ stripVTControlCharacters }=require('util');
 
 constinput=['const foo = {','};','foo'];
 
 functionrun({ useColors }){
 const{ replServer, output }=startNewREPLServer({ useColors });
 
 replServer.on('exit',common.mustCall(()=>{
-constactual=output.accumulator.split('\n');
+// The output contains various escape codes, including
+// screen clears and others, so we trim them all to
+// simplify this test.
+constactual=stripVTControlCharacters(output.accumulator);
 
-// Validate the output, which contains terminal escape codes.
-assert.strictEqual(actual.length,6);
-assert.ok(actual[0].endsWith(input[0]));
-assert.ok(actual[1].includes('| '));
-assert.ok(actual[1].endsWith(input[1]));
-assert.ok(actual[2].includes('undefined'));
-assert.ok(actual[3].endsWith(input[2]));
-assert.strictEqual(actual[4],'{}');
+constfirstStatementIdx=actual.indexOf(input.slice(0,1).join('\n| '));
+assert(firstStatementIdx>-1);
+
+assert(actual.slice(firstStatementIdx).includes('undefined'));
+assert(actual.slice(firstStatementIdx).includes('foo'));
 }));
 
 input.forEach((line)=>replServer.write(`${line}\n`));

test/parallel/test-repl-preview-newlines.js

@@ -6,7 +6,14 @@ const { startNewREPLServer } = require('../common/repl');
 
 common.skipIfInspectorDisabled();
 
-const{ input, output }=startNewREPLServer({useColors: true});
+// Ignore terminal settings so the preview remains active under TERM=dumb.
+process.env.TERM='';
+
+// Keep syntax highlighting out of this test so it only covers preview layout.
+// Preview and result colors are enabled after readline is initialized.
+const{ input, output, replServer }=startNewREPLServer({useColors: false});
+replServer.useColors=true;
+replServer.writer.options.colors=true;
 
 output.accumulator='';
 

test/parallel/test-repl-preview-without-inspector.js

@@ -69,9 +69,13 @@ const repl = new REPLServer({
 prompt: PROMPT,
 stream: newREPLStream(),
 ignoreUndefined: true,
-useColors: true,
+// Keep syntax highlighting out of these preview transcript assertions.
+// Preview and result colors are enabled after readline is initialized.
+useColors: false,
 terminal: true,
 });
+repl.useColors=true;
+repl.writer.options.colors=true;
 
 repl.inputStream.run([
 'function foo(x) { return x; }',

test/parallel/test-repl-preview.js

@@ -61,9 +61,13 @@ async function tests(options) {
 prompt: PROMPT,
 stream: newREPLStream(),
 ignoreUndefined: true,
-useColors: true,
+// Keep syntax highlighting out of these preview transcript assertions.
+// Preview and result colors are enabled after readline is initialized.
+useColors: false,
  ...options
 });
+repl.useColors=true;
+repl.writer.options.colors=true;
 
 repl.inputStream.run([
 'function foo(x) { return x; }',

test/parallel/test-repl-reverse-search.js

@@ -329,7 +329,9 @@ function runTest() {
 }),
 completer: opts.completer,
  prompt,
-useColors: opts.useColors||false,
+// Keep syntax highlighting out of the reverse-search transcript. Result
+// colors are enabled below after readline has been initialized.
+useColors: false,
 terminal: true
 },common.mustCall((err,repl)=>{
 if(err){
@@ -351,6 +353,11 @@ function runTest() {
 setImmediate(runTestWrap,true);
 }));
 
+if(opts.useColors){
+repl.useColors=true;
+repl.writer.options.colors=true;
+}
+
 if(opts.columns){
 Object.defineProperty(repl,'columns',{
 value: opts.columns,