workers: replace message types string by constants

This change can prevent typos and redundant strings in code.
PR-URL: #21537
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

Author: starkwang

lib/internal/worker.js

@@ -47,6 +47,15 @@ const kIncrementsPortRef = Symbol('kIncrementsPortRef');
 
 constdebug=util.debuglog('worker');
 
+constmessageTypes={
+UP_AND_RUNNING: 'upAndRunning',
+COULD_NOT_SERIALIZE_ERROR: 'couldNotSerializeError',
+ERROR_MESSAGE: 'errorMessage',
+STDIO_PAYLOAD: 'stdioPayload',
+STDIO_WANTS_MORE_DATA: 'stdioWantsMoreData',
+LOAD_SCRIPT: 'loadScript'
+};
+
 // A communication channel consisting of a handle (that wraps around an
 // uv_async_t) which can receive information from other threads and emits
 // .onmessage events, and a function used for sending data to a MessagePort
@@ -158,7 +167,7 @@ class ReadableWorkerStdio extends Readable {
 }
 
 this[kPort].postMessage({
-type: 'stdioWantsMoreData',
+type: messageTypes.STDIO_WANTS_MORE_DATA,
 stream: this[kName]
 });
 }
@@ -174,7 +183,7 @@ class WritableWorkerStdio extends Writable {
 
 _write(chunk,encoding,cb){
 this[kPort].postMessage({
-type: 'stdioPayload',
+type: messageTypes.STDIO_PAYLOAD,
 stream: this[kName],
  chunk,
  encoding
@@ -186,7 +195,7 @@ class WritableWorkerStdio extends Writable {
 
 _final(cb){
 this[kPort].postMessage({
-type: 'stdioPayload',
+type: messageTypes.STDIO_PAYLOAD,
 stream: this[kName],
 chunk: null
 });
@@ -258,7 +267,7 @@ class Worker extends EventEmitter {
 this[kPublicPort].on('message',(message)=>this.emit('message',message));
 setupPortReferencing(this[kPublicPort],this,'message');
 this[kPort].postMessage({
-type: 'loadScript',
+type: messageTypes.LOAD_SCRIPT,
  filename,
 doEval: !!options.eval,
 workerData: options.workerData,
@@ -289,18 +298,18 @@ class Worker extends EventEmitter {
 
 [kOnMessage](message){
 switch(message.type){
-case'upAndRunning':
+casemessageTypes.UP_AND_RUNNING:
 returnthis.emit('online');
-case'couldNotSerializeError':
+casemessageTypes.COULD_NOT_SERIALIZE_ERROR:
 returnthis[kOnCouldNotSerializeErr]();
-case'errorMessage':
+casemessageTypes.ERROR_MESSAGE:
 returnthis[kOnErrorMessage](message.error);
-case'stdioPayload':
+casemessageTypes.STDIO_PAYLOAD:
 {
 const{ stream, chunk, encoding }=message;
 returnthis[kParentSideStdio][stream].push(chunk,encoding);
 }
-case'stdioWantsMoreData':
+casemessageTypes.STDIO_WANTS_MORE_DATA:
 {
 const{ stream }=message;
 returnthis[kParentSideStdio][stream][kStdioWantsMoreDataCallback]();
@@ -396,7 +405,7 @@ function setupChild(evalScript) {
 constpublicWorker=require('worker_threads');
 
 port.on('message',(message)=>{
-if(message.type==='loadScript'){
+if(message.type===messageTypes.LOAD_SCRIPT){
 const{ filename, doEval, workerData, publicPort, hasStdin }=message;
 publicWorker.parentPort=publicPort;
 setupPortReferencing(publicPort,publicPort,'message');
@@ -408,19 +417,19 @@ function setupChild(evalScript) {
 debug(`[${threadId}] starts worker script ${filename} `+
 `(eval = ${eval}) at cwd = ${process.cwd()}`);
 port.unref();
-port.postMessage({type: 'upAndRunning'});
+port.postMessage({type: messageTypes.UP_AND_RUNNING});
 if(doEval){
 evalScript('[worker eval]',filename);
 }else{
 process.argv[1]=filename;// script filename
 require('module').runMain();
 }
 return;
-}elseif(message.type==='stdioPayload'){
+}elseif(message.type===messageTypes.STDIO_PAYLOAD){
 const{ stream, chunk, encoding }=message;
 workerStdio[stream].push(chunk,encoding);
 return;
-}elseif(message.type==='stdioWantsMoreData'){
+}elseif(message.type===messageTypes.STDIO_WANTS_MORE_DATA){
 const{ stream }=message;
 workerStdio[stream][kStdioWantsMoreDataCallback]();
 return;
@@ -451,9 +460,12 @@ function setupChild(evalScript) {
 }catch{}
 debug(`[${threadId}] fatal exception serialized = ${!!serialized}`);
 if(serialized)
-port.postMessage({type: 'errorMessage',error: serialized});
+port.postMessage({
+type: messageTypes.ERROR_MESSAGE,
+error: serialized
+});
 else
-port.postMessage({type: 'couldNotSerializeError'});
+port.postMessage({type: messageTypes.COULD_NOT_SERIALIZE_ERROR});
 clearAsyncIdStack();
 }
 }