Use Object.assign in a few more places. NFC (#15823)

Followup to #15822

Author: sbc100

src/library.js

@@ -3329,10 +3329,8 @@ LibraryManager.library = {
 #endif
     var argCache = [];
     return function() {
-      argCache.length = arguments.length;
-      for (var i = 0; i < arguments.length; i++) {
-        argCache[i] = arguments[i];
-      }
+      argCache.length = 0;
+      Object.assign(argCache, arguments);
       return dynCall(sig, ptr, argCache);
     };
   },

src/library_fs.js

@@ -422,11 +422,7 @@ FS.staticInit();` +
         };
       }
       // clone it, so we can return an instance of FSStream
-      var newStream = new FS.FSStream();
-      for (var p in stream) {
-        newStream[p] = stream[p];
-      }
-      stream = newStream;
+      stream = Object.assign(new FS.FSStream(), stream);
       var fd = FS.nextfd(fd_start, fd_end);
       stream.fd = fd;
       FS.streams[fd] = stream;

src/library_pthread.js

@@ -161,9 +161,7 @@ var LibraryPThread = {
     receiveObjectTransfer: function(data) {
 #if OFFSCREENCANVAS_SUPPORT
       if (typeof GL !== 'undefined') {
-        for (var i in data.offscreenCanvases) {
-          GL.offscreenCanvases[i] = data.offscreenCanvases[i];
-        }
+        Object.assign(GL.offscreenCanvases, data.offscreenCanvases);
         if (!Module['canvas'] && data.moduleCanvasId && GL.offscreenCanvases[data.moduleCanvasId]) {
           Module['canvas'] = GL.offscreenCanvases[data.moduleCanvasId].offscreenCanvas;
           Module['canvas'].id = data.moduleCanvasId;

src/shell_minimal.js

@@ -125,6 +125,13 @@ function ready() {
 #endif
 }
 
+#if POLYFILL
+// See https://caniuse.com/mdn-javascript_builtins_object_assign
+#if MIN_CHROME_VERSION < 45 || MIN_EDGE_VERSION < 12 || MIN_FIREFOX_VERSION < 34 || MIN_IE_VERSION != TARGET_NOT_SUPPORTED || MIN_SAFARI_VERSION < 90000
+#include "polyfill/objassign.js"
+#endif
+#endif
+
 // --pre-jses are emitted after the Module integration code, so that they can
 // refer to Module (if they choose; they can also define Module)
 

tests/other/metadce/hello_libcxx_O2.jssize

@@ -1 +1 @@
-96785
+96720

tests/other/metadce/hello_libcxx_O2_EVAL_CTORS.jssize

@@ -1 +1 @@
-96785
+96720

tests/other/metadce/hello_libcxx_O2_EVAL_CTORS_2.jssize

@@ -1 +1 @@
-96683
+96618

tests/other/metadce/hello_libcxx_O2_fexceptions.jssize

@@ -1 +1 @@
-110239
+110174

tests/other/metadce/hello_libcxx_O2_fexceptions_DEMANGLE_SUPPORT.jssize

@@ -1 +1 @@
-111226
+111161

tests/other/metadce/hello_world_O3_MAIN_MODULE_2.jssize

@@ -1 +1 @@
-97046
+96981