fix #951: lower object rest and spread for v8

CHANGELOG.md

@@ -14,6 +14,10 @@
 
     Previously conditional CSS imports such as `@import "print.css" print;` was not supported at all and was considered a syntax error. With this release, it is now supported in all cases except when bundling an internal import. Support for bundling internal CSS imports is planned but will happen in a later release.
 
+* Always lower object spread and rest when targeting V8 ([#951](https://github.com/evanw/esbuild/issues/951))
+
+    This release causes object spread (e.g. `a = {...b}`) and object rest (e.g. `{...a} = b`) to always be lowered to a manual implementation instead of using native syntax when the `--target=` parameter includes a V8-based JavaScript runtime such as `chrome`, `edge`, or `node`. It turns out this feature is implemented inefficiently in V8 and copying properties over to a new object is around a 2x performance improvement. In addition, doing this manually instead of using the native implementation generates a lot less work for the garbage collector. You can see [V8 bug 11536](https://bugs.chromium.org/p/v8/issues/detail?id=11536) for details. If the V8 performance bug is eventually fixed, the translation of this syntax will be disabled again for V8-based targets containing the bug fix.
+
 ## 0.9.0
 
 **This release contains backwards-incompatible changes.** Since esbuild is before version 1.0.0, these changes have been released as a new minor version to reflect this (as [recommended by npm](https://docs.npmjs.com/cli/v6/using-npm/semver/)). You should either be pinning the exact version of `esbuild` in your `package.json` file or be using a version range syntax that only accepts patch upgrades such as `^0.8.0`. See the documentation about [semver](https://docs.npmjs.com/cli/v6/using-npm/semver/) for more information.

internal/compat/js_table.go

@@ -313,12 +313,9 @@ var jsTable = map[JSFeature]map[Engine][]int{
 		Safari:  {7, 1},
 	},
 	ObjectRestSpread: {
-		Chrome:  {60},
-		Edge:    {79},
 		ES:      {2018},
 		Firefox: {55},
 		IOS:     {11, 3},
-		Node:    {8, 3},
 		Safari:  {11, 1},
 	},
 	OptionalCatchBinding: {

scripts/compat-table.js

@@ -177,6 +177,13 @@ for (const test of [...es5.tests, ...es6.tests, ...stage4.tests, ...stage1to3.te
   }
 }
 
+// Work around V8-specific issues
+for (const v8 of ['chrome', 'edge', 'node']) {
+  // Always lower object rest and spread for V8-based JavaScript VMs because of
+  // a severe performance issue: https://bugs.chromium.org/p/v8/issues/detail?id=11536
+  delete versions.ObjectRestSpread[v8]
+}
+
 for (const feature in features) {
   if (!features[feature].found) {
     throw new Error(`Did not find ${feature}`)