fix #4310: add Iterator and other known globals

Author: evanw

CHANGELOG.md

@@ -6,6 +6,33 @@
 
     The previous release introduced support for parsing media queries which unintentionally introduced a regression with the removal of duplicate media rules during minification. Specifically the grammar for `@media <media-type> and <media-condition-without-or> { ... }` was missing an equality check for the `<media-condition-without-or>` part, so rules with different suffix clauses in this position would incorrectly compare equal and be deduplicated. This release fixes the regression.
 
+* Update the list of known JavaScript globals ([#4310](https://github.com/evanw/esbuild/issues/4310))
+
+    This release updates esbuild's internal list of known JavaScript globals. These are globals that are known to not have side-effects when the property is accessed. For example, accessing the global `Array` property is considered to be side-effect free but accessing the global `scrollY` property can trigger a layout, which is a side-effect. This is used by esbuild's tree-shaking to safely remove unused code that is known to be side-effect free. This update adds the following global properties:
+
+    From [ES2017](https://tc39.es/ecma262/2017/):
+    - `Atomics`
+    - `SharedArrayBuffer`
+
+    From [ES2020](https://tc39.es/ecma262/2020/):
+    - `BigInt64Array`
+    - `BigUint64Array`
+
+    From [ES2021](https://tc39.es/ecma262/2021/):
+    - `FinalizationRegistry`
+    - `WeakRef`
+
+    From [ES2025](https://tc39.es/ecma262/2025/):
+    - `Float16Array`
+    - `Iterator`
+
+    Note that this does not indicate that constructing any of these objects is side-effect free, just that accessing the identifier is side-effect free. For example, this now allows esbuild to tree-shake classes that extend from `Iterator`:
+
+    ```js
+    // This can now be tree-shaken by esbuild:
+    class ExampleIterator extends Iterator {}
+    ```
+
 * Add support for the new `@view-transition` CSS rule ([#4313](https://github.com/evanw/esbuild/pull/4313))
 
     With this release, esbuild now has improved support for pretty-printing and minifying the new `@view-transition` rule (which esbuild was previously unaware of):

internal/bundler_tests/bundler_dce_test.go

@@ -4930,3 +4930,20 @@ func TestDCEOfNegatedBigints(t *testing.T) {
 		},
 	})
 }
+
+// https://github.com/evanw/esbuild/issues/4310
+func TestDCEOfIteratorSuperclassIssue4310(t *testing.T) {
+	dce_suite.expectBundled(t, bundled{
+		files: map[string]string{
+			"/entry.js": `
+				class Keep extends NotIterator {}
+				class Remove extends Iterator {}
+			`,
+		},
+		entryPaths: []string{"/entry.js"},
+		options: config.Options{
+			Mode:         config.ModeBundle,
+			AbsOutputDir: "/out",
+		},
+	})
+}

internal/bundler_tests/snapshots/snapshots_dce.txt

@@ -652,6 +652,13 @@ use(isNotPure);
   } };
 })();
 
+================================================================================
+TestDCEOfIteratorSuperclassIssue4310
+---------- /out/entry.js ----------
+// entry.js
+var Keep = class extends NotIterator {
+};
+
 ================================================================================
 TestDCEOfNegatedBigints
 ---------- /out/entry.js ----------

internal/config/globals.go

@@ -27,18 +27,6 @@ var processedGlobals *ProcessedDefines
 // these functions has any side effects. It only says something about
 // referencing these function without calling them.
 var knownGlobals = [][]string{
-	// These global identifiers should exist in all JavaScript environments. This
-	// deliberately omits "NaN", "Infinity", and "undefined" because these are
-	// treated as automatically-inlined constants instead of identifiers.
-	{"Array"},
-	{"Boolean"},
-	{"Function"},
-	{"Math"},
-	{"Number"},
-	{"Object"},
-	{"RegExp"},
-	{"String"},
-
 	// Object: Static methods
 	// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object#Static_methods
 	{"Object", "assign"},
@@ -166,36 +154,57 @@ var knownGlobals = [][]string{
 	{"JSON", "parse"},
 	{"JSON", "stringify"},
 
-	// Other globals present in both the browser and node (except "eval" because
-	// it has special behavior)
+	// Other globals present in both the browser and node. This should include at
+	// least the following properties:
+	// https://tc39.es/ecma262/multipage/global-object.html#sec-constructor-properties-of-the-global-object
+	//
+	// Exceptions:
+	// - Don't include "eval" because it has special behavior
+	// - Don't include "NaN", "Infinity", and "undefined" because esbuild treats
+	//   these as automatically-inlined constants instead of identifiers
 	{"AbortController"},
 	{"AbortSignal"},
 	{"AggregateError"},
+	{"Array"},
 	{"ArrayBuffer"},
+	{"Atomics"},
 	{"BigInt"},
+	{"BigInt64Array"},
+	{"BigUint64Array"},
+	{"Boolean"},
 	{"DataView"},
 	{"Date"},
 	{"Error"},
 	{"EvalError"},
 	{"Event"},
 	{"EventTarget"},
+	{"FinalizationRegistry"},
+	{"Float16Array"},
 	{"Float32Array"},
 	{"Float64Array"},
+	{"Function"},
 	{"Int16Array"},
 	{"Int32Array"},
 	{"Int8Array"},
 	{"Intl"},
+	{"Iterator"},
 	{"JSON"},
 	{"Map"},
+	{"Math"},
 	{"MessageChannel"},
 	{"MessageEvent"},
 	{"MessagePort"},
+	{"Number"},
+	{"Object"},
 	{"Promise"},
 	{"Proxy"},
 	{"RangeError"},
 	{"ReferenceError"},
 	{"Reflect"},
+	{"RegExp"},
 	{"Set"},
+	{"SharedArrayBuffer"},
+	{"String"},
 	{"Symbol"},
 	{"SyntaxError"},
 	{"TextDecoder"},
@@ -209,6 +218,7 @@ var knownGlobals = [][]string{
 	{"Uint8Array"},
 	{"Uint8ClampedArray"},
 	{"WeakMap"},
+	{"WeakRef"},
 	{"WeakSet"},
 	{"WebAssembly"},
 	{"clearInterval"},