Intiial usage of arrow function (=>) in JS library code

Now that arrow functions and `let`/`const` are permitted in
emscripten JS library code we can take advantage of this to
reduce the size of the JS code that we output by default.

Followup to #15764

See: #11984

Author: sbc100

emcc.py

@@ -3340,7 +3340,7 @@ def modularize():
     return_value = '{}'
 
   src = '''
-function(%(EXPORT_NAME)s) {
+(%(EXPORT_NAME)s) => {
   %(EXPORT_NAME)s = %(EXPORT_NAME)s || {};
 
 %(src)s
@@ -3370,7 +3370,7 @@ def modularize():
       if shared.target_environment_may_be('node'):
         script_url_node = "if (typeof __filename !== 'undefined') _scriptDir = _scriptDir || __filename;"
     src = '''
-var %(EXPORT_NAME)s = (function() {
+var %(EXPORT_NAME)s = (() => {
   var _scriptDir = %(script_url)s;
   %(script_url_node)s
   return (%(src)s);

src/library.js

@@ -325,14 +325,12 @@ LibraryManager.library = {
       var cp = require('child_process');
       var ret = cp.spawnSync(cmdstr, [], {shell:true, stdio:'inherit'});
 
-      var _W_EXITCODE = function(ret, sig) {
-        return ((ret) << 8 | (sig));
-      }
+      var _W_EXITCODE = (ret, sig) => ((ret) << 8 | (sig));
 
       // this really only can happen if process is killed by signal
       if (ret.status === null) {
         // sadly node doesn't expose such function
-        var signalToNumber = function(sig) {
+        var signalToNumber = (sig) => {
           // implement only the most common ones, and fallback to SIGINT
           switch (sig) {
             case 'SIGHUP': return 1;
@@ -1177,7 +1175,7 @@ LibraryManager.library = {
       var date = initDate();
       var value;
 
-      var getMatch = function(symbol) {
+      var getMatch = (symbol) => {
         var pos = capture.indexOf(symbol);
         // check if symbol appears in regexp
         if (pos >= 0) {
@@ -2530,7 +2528,7 @@ LibraryManager.library = {
   emscripten_get_now: ';' +
 #if ENVIRONMENT_MAY_BE_NODE
                                "if (ENVIRONMENT_IS_NODE) {\n" +
-                               "  _emscripten_get_now = function() {\n" +
+                               "  _emscripten_get_now = () => {\n" +
                                "    var t = process['hrtime']();\n" +
                                "    return t[0] * 1e3 + t[1] / 1e6;\n" +
                                "  };\n" +
@@ -2539,7 +2537,7 @@ LibraryManager.library = {
 #if USE_PTHREADS
 // Pthreads need their clocks synchronized to the execution of the main thread, so give them a special form of the function.
                                "if (ENVIRONMENT_IS_PTHREAD) {\n" +
-                               "  _emscripten_get_now = function() { return performance.now() - Module['__performance_now_clock_drift']; };\n" +
+                               "  _emscripten_get_now = () => performance.now() - Module['__performance_now_clock_drift'];\n" +
                                "} else " +
 #endif
 #if ENVIRONMENT_MAY_BE_SHELL
@@ -2549,14 +2547,14 @@ LibraryManager.library = {
 #endif
 #if MIN_IE_VERSION <= 9 || MIN_FIREFOX_VERSION <= 14 || MIN_CHROME_VERSION <= 23 || MIN_SAFARI_VERSION <= 80400 // https://caniuse.com/#feat=high-resolution-time
                                "if (typeof performance !== 'undefined' && performance.now) {\n" +
-                               "  _emscripten_get_now = function() { return performance.now(); }\n" +
+                               "  _emscripten_get_now = () => performance.now();\n" +
                                "} else {\n" +
                                "  _emscripten_get_now = Date.now;\n" +
                                "}",
 #else
                                // Modern environment where performance.now() is supported:
                                // N.B. a shorter form "_emscripten_get_now = return performance.now;" is unfortunately not allowed even in current browsers (e.g. FF Nightly 75).
-                               "_emscripten_get_now = function() { return performance.now(); }\n",
+                               "_emscripten_get_now = () => performance.now();\n",
 #endif
 
   emscripten_get_now_res: function() { // return resolution of get_now, in nanoseconds

src/library_browser.js

@@ -150,7 +150,7 @@ var LibraryBrowser = {
         assert(typeof url == 'string', 'createObjectURL must return a url as a string');
 #endif
         var img = new Image();
-        img.onload = function img_onload() {
+        img.onload = () => {
           assert(img.complete, 'Image ' + name + ' could not be decoded');
           var canvas = document.createElement('canvas');
           canvas.width = img.width;
@@ -161,7 +161,7 @@ var LibraryBrowser = {
           Browser.URLObject.revokeObjectURL(url);
           if (onload) onload(byteArray);
         };
-        img.onerror = function img_onerror(event) {
+        img.onerror = (event) => {
           out('Image ' + url + ' could not be decoded');
           if (onerror) onerror();
         };

src/library_webgl.js

@@ -675,7 +675,7 @@ var LibraryGL = {
 #endif
 
 #if GL_DISABLE_HALF_FLOAT_EXTENSION_IF_BROKEN
-      function disableHalfFloatExtensionIfBroken(ctx) {
+      const disableHalfFloatExtensionIfBroken = (ctx) => {
         var t = ctx.createTexture();
         ctx.bindTexture(0xDE1/*GL_TEXTURE_2D*/, t);
         for (var i = 0; i < 8 && ctx.getError(); ++i) /*no-op*/;

src/preamble_minimal.js

@@ -29,12 +29,8 @@ var tempI64;
 #endif
 
 var tempRet0 = 0;
-var setTempRet0 = function(value) {
-  tempRet0 = value;
-}
-var getTempRet0 = function() {
-  return tempRet0;
-}
+var setTempRet0 = (value) => { tempRet0 = value };
+var getTempRet0 = () => tempRet0;
 
 function alignUp(x, multiple) {
   if (x % multiple > 0) {

src/proxyClient.js

@@ -205,7 +205,7 @@ worker.onmessage = function worker_onmessage(event) {
     case 'Image': {
       assert(data.method === 'src');
       var img = new Image();
-      img.onload = function() {
+      img.onload = () => {
         assert(img.complete);
         var canvas = document.createElement('canvas');
         canvas.width = img.width;
@@ -215,7 +215,7 @@ worker.onmessage = function worker_onmessage(event) {
         var imageData = ctx.getImageData(0, 0, img.width, img.height);
         worker.postMessage({ target: 'Image', method: 'onload', id: data.id, width: img.width, height: img.height, data: imageData.data, preMain: true });
       };
-      img.onerror = function() {
+      img.onerror = () => {
         worker.postMessage({ target: 'Image', method: 'onerror', id: data.id, preMain: true });
       };
       img.src = data.src;

src/runtime_strings.js

@@ -17,7 +17,7 @@
 // character.
 function TextDecoderWrapper(encoding) {
   var textDecoder = new TextDecoder(encoding);
-  this.decode = function(data) {
+  this.decode = (data) => {
 #if ASSERTIONS
     assert(data instanceof Uint8Array);
 #endif

src/shell.js

@@ -68,9 +68,7 @@ var moduleOverrides = Object.assign({}, Module);
 
 var arguments_ = [];
 var thisProgram = './this.program';
-var quit_ = function(status, toThrow) {
-  throw toThrow;
-};
+var quit_ = (status, toThrow) => { throw toThrow; };
 
 // Determine the runtime environment we are in. You can customize this by
 // setting the ENVIRONMENT setting at compile time (see settings.js).
@@ -157,7 +155,7 @@ var read_,
 // this may no longer be needed under node.
 function logExceptionOnExit(e) {
   if (e instanceof ExitStatus) return;
-  var toLog = e;
+  let toLog = e;
 #if ASSERTIONS
   if (e && typeof e === 'object' && e.stack) {
     toLog = [e, e.stack];
@@ -218,7 +216,7 @@ if (ENVIRONMENT_IS_NODE) {
   process['on']('unhandledRejection', function(reason) { throw reason; });
 #endif
 
-  quit_ = function(status, toThrow) {
+  quit_ = (status, toThrow) => {
     if (keepRuntimeAlive()) {
       process['exitCode'] = status;
       throw toThrow;
@@ -230,7 +228,7 @@ if (ENVIRONMENT_IS_NODE) {
   Module['inspect'] = function () { return '[Emscripten Module object]'; };
 
 #if USE_PTHREADS
-  var nodeWorkerThreads;
+  let nodeWorkerThreads;
   try {
     nodeWorkerThreads = require('worker_threads');
   } catch (e) {
@@ -262,7 +260,7 @@ if (ENVIRONMENT_IS_SHELL) {
   if (typeof read != 'undefined') {
     read_ = function shell_read(f) {
 #if SUPPORT_BASE64_EMBEDDING
-      var data = tryParseAsDataURI(f);
+      const data = tryParseAsDataURI(f);
       if (data) {
         return intArrayToString(data);
       }
@@ -272,7 +270,7 @@ if (ENVIRONMENT_IS_SHELL) {
   }
 
   readBinary = function readBinary(f) {
-    var data;
+    let data;
 #if SUPPORT_BASE64_EMBEDDING
     data = tryParseAsDataURI(f);
     if (data) {
@@ -288,7 +286,7 @@ if (ENVIRONMENT_IS_SHELL) {
   };
 
   readAsync = function readAsync(f, onload, onerror) {
-    setTimeout(function() { onload(readBinary(f)); }, 0);
+    setTimeout(() => onload(readBinary(f)), 0);
   };
 
   if (typeof scriptArgs != 'undefined') {
@@ -298,7 +296,7 @@ if (ENVIRONMENT_IS_SHELL) {
   }
 
   if (typeof quit === 'function') {
-    quit_ = function(status, toThrow) {
+    quit_ = (status, toThrow) => {
       logExceptionOnExit(toThrow);
       quit(status);
     };
@@ -371,7 +369,7 @@ if (ENVIRONMENT_IS_WEB || ENVIRONMENT_IS_WORKER) {
 
   }
 
-  setWindowTitle = function(title) { document.title = title };
+  setWindowTitle = (title) => document.title = title;
 } else
 #endif // ENVIRONMENT_MAY_BE_WEB || ENVIRONMENT_MAY_BE_WORKER
 {
@@ -399,8 +397,8 @@ var defaultPrint = console.log.bind(console);
 var defaultPrintErr = console.warn.bind(console);
 if (ENVIRONMENT_IS_NODE) {
   requireNodeFS();
-  defaultPrint = function(str) { fs.writeSync(1, str + '\n'); };
-  defaultPrintErr = function(str) { fs.writeSync(2, str + '\n'); };
+  defaultPrint = (str) => fs.writeSync(1, str + '\n');
+  defaultPrintErr = (str) => fs.writeSync(2, str + '\n');
 }
 {{{ makeModuleReceiveWithVar('out', 'print',    'defaultPrint',    true) }}}
 {{{ makeModuleReceiveWithVar('err', 'printErr', 'defaultPrintErr', true) }}}

src/shell_minimal.js

@@ -15,7 +15,7 @@ var Module = {{{ EXPORT_NAME }}};
 #if MODULARIZE && EXPORT_READY_PROMISE
 // Set up the promise that indicates the Module is initialized
 var readyPromiseResolve, readyPromiseReject;
-Module['ready'] = new Promise(function(resolve, reject) {
+Module['ready'] = new Promise((resolve, reject) => {
   readyPromiseResolve = resolve;
   readyPromiseReject = reject;
 });

tests/code_size/hello_webgl2_wasm.json

@@ -1,10 +1,10 @@
 {
   "a.html": 569,
   "a.html.gz": 379,
-  "a.js": 5000,
-  "a.js.gz": 2422,
+  "a.js": 4968,
+  "a.js.gz": 2418,
   "a.wasm": 10442,
   "a.wasm.gz": 6661,
-  "total": 16011,
-  "total_gz": 9462
+  "total": 15979,
+  "total_gz": 9458
 }