esm: disable non-js exts outside package scopes

PR-URL: #30501
Reviewed-By: Jan Krems <jan.krems@gmail.com>
Reviewed-By: Myles Borins <myles.borins@gmail.com>

Author: guybedford

doc/api/esm.md

@@ -1310,8 +1310,7 @@ _defaultEnv_ is the conditional environment name priority array,
 > 1. Return _"module"_.
 > 1. Throw an _Unsupported File Extension_ error.
 > 1. Otherwise,
-> 1. If _isMain_ is **true** or _url_ ends in _".js"_, _".json"_ or
-> _".node"_, then
+> 1. If _isMain_ is **true**, then
 > 1. Return _"commonjs"_.
 > 1. Throw an _Unsupported File Extension_ error.
 

lib/internal/modules/esm/default_resolve.js

@@ -78,9 +78,19 @@ function resolve(specifier, parentURL) {
 }
 
 constisMain=parentURL===undefined;
-if(isMain)
+if(isMain){
 parentURL=pathToFileURL(`${process.cwd()}/`).href;
 
+// This is the initial entry point to the program, and --input-type has
+// been passed as an option; but --input-type can only be used with
+// --eval, --print or STDIN string input. It is not allowed with file
+// input, to avoid user confusion over how expansive the effect of the
+// flag should be (i.e. entry point only, package scope surrounding the
+// entry point, etc.).
+if(typeFlag)
+thrownewERR_INPUT_TYPE_NOT_ALLOWED();
+}
+
 leturl=moduleWrapResolve(specifier,parentURL);
 
 if(isMain ? !preserveSymlinksMain : !preserveSymlinks){
@@ -93,27 +103,13 @@ function resolve(specifier, parentURL) {
 url.hash=old.hash;
 }
 
-consttype=getPackageType(url.href);
-
 constext=extname(url.pathname);
-constextMap=
-type!==TYPE_MODULE ? legacyExtensionFormatMap : extensionFormatMap;
-letformat=extMap[ext];
-
-if(isMain&&typeFlag){
-// This is the initial entry point to the program, and --input-type has
-// been passed as an option; but --input-type can only be used with
-// --eval, --print or STDIN string input. It is not allowed with file
-// input, to avoid user confusion over how expansive the effect of the
-// flag should be (i.e. entry point only, package scope surrounding the
-// entry point, etc.).
-thrownewERR_INPUT_TYPE_NOT_ALLOWED();
-}
+letformat=extensionFormatMap[ext];
+if(ext==='.js'||(!format&&isMain))
+format=getPackageType(url.href)===TYPE_MODULE ? 'module' : 'commonjs';
 if(!format){
-if(isMain)
-format=type===TYPE_MODULE ? 'module' : 'commonjs';
-elseif(esModuleSpecifierResolution==='node')
-format='commonjs';
+if(esModuleSpecifierResolution==='node')
+format=legacyExtensionFormatMap[ext];
 else
 thrownewERR_UNKNOWN_FILE_EXTENSION(fileURLToPath(url));
 }

test/es-module/test-esm-non-js.js

@@ -0,0 +1,21 @@
+'use strict';
+
+constcommon=require('../common');
+const{ spawn }=require('child_process');
+constassert=require('assert');
+
+constentry=require.resolve('./test-esm-json.mjs');
+
+// Verify non-js extensions fail for ESM
+constchild=spawn(process.execPath,['--experimental-modules',entry]);
+
+letstderr='';
+child.stderr.setEncoding('utf8');
+child.stderr.on('data',(data)=>{
+stderr+=data;
+});
+child.on('close',common.mustCall((code,signal)=>{
+assert.strictEqual(code,1);
+assert.strictEqual(signal,null);
+assert.ok(stderr.indexOf('ERR_UNKNOWN_FILE_EXTENSION')!==-1);
+}));