perf: improve

alexander-akait · web-flow · commit 8ed6d8a627c1 · 2026-04-29T18:48:27.000+03:00
diff --git a/benchmark/cases/replace-source/index.bench.mjs b/benchmark/cases/replace-source/index.bench.mjs
@@ -147,12 +147,18 @@ export default function register(bench) {
 	});
 
 	bench.add("replace-source: getReplacements()", () => {
-		buildManyReplacements(1000).getReplacements();
+		const src = buildManyReplacements(1000);
+		let sink = 0;
+		for (let i = 0; i < 50_000; i++) sink ^= src.getReplacements().length;
+		if (sink === -1) throw new Error("unreachable");
 	});
 
 	bench.add("replace-source: original()", () => {
 		const src = new sources.ReplaceSource(new sources.RawSource(fixtureCode));
-		for (let i = 0; i < 500; i++) src.original();
+		const inner = src.original();
+		let sink = 0;
+		for (let i = 0; i < 50_000; i++) sink ^= src.original() === inner ? 1 : 0;
+		if (sink === -1) throw new Error("unreachable");
 	});
 
 	bench.add("replace-source: updateHash()", () => {
diff --git a/lib/ConcatSource.js b/lib/ConcatSource.js
@@ -38,10 +38,15 @@ class ConcatSource extends Source {
 		 */
 		this._children = [];
 
-		for (const item of args) {
+		// Indexed loops avoid the iterator-protocol overhead `for...of`
+		// pays per element. Hot during webpack's emit when many
+		// ConcatSources are constructed/flattened.
+		for (let i = 0, l = args.length; i < l; i++) {
+			const item = args[i];
 			if (item instanceof ConcatSource) {
-				for (const child of item._children) {
-					this._children.push(child);
+				const children = item._children;
+				for (let j = 0, jl = children.length; j < jl; j++) {
+					this._children.push(children[j]);
 				}
 			} else {
 				this._children.push(item);
@@ -69,8 +74,9 @@ class ConcatSource extends Source {
 	 */
 	add(item) {
 		if (item instanceof ConcatSource) {
-			for (const child of item._children) {
-				this._children.push(child);
+			const children = item._children;
+			for (let i = 0, l = children.length; i < l; i++) {
+				this._children.push(children[i]);
 			}
 		} else {
 			this._children.push(item);
@@ -83,8 +89,8 @@ class ConcatSource extends Source {
 	 * @returns {void}
 	 */
 	addAllSkipOptimizing(items) {
-		for (const item of items) {
-			this._children.push(item);
+		for (let i = 0, l = items.length; i < l; i++) {
+			this._children.push(items[i]);
 		}
 	}
 
@@ -197,7 +203,10 @@ class ConcatSource extends Source {
 		const finalSource = Boolean(options && options.finalSource);
 		let code = "";
 		let needToCloseMapping = false;
-		for (const item of /** @type {Source[]} */ (this._children)) {
+		const children = /** @type {Source[]} */ (this._children);
+		const childCount = children.length;
+		for (let ci = 0; ci < childCount; ci++) {
+			const item = children[ci];
 			/** @type {number[]} */
 			const sourceIndexMapping = [];
 			/** @type {number[]} */
@@ -391,7 +400,9 @@ class ConcatSource extends Source {
 				newChildren.push(currentRawSources);
 			}
 		};
-		for (const child of this._children) {
+		const children = this._children;
+		for (let ci = 0, cl = children.length; ci < cl; ci++) {
+			const child = children[ci];
 			if (typeof child === "string") {
 				if (currentString === undefined) {
 					currentString = child;
