perf: avoid create uncessary overrides for replace

Author: antfu

README.md

@@ -193,7 +193,7 @@ The differences from [`String.replace`]((https://developer.mozilla.org/en-US/doc
 ### s.replaceAll( regexpOrString, substitution )
 
 Same as `s.replace`, but replace all matched strings instead of just one.
-If `substitution` is a regex, then it must have the global (`g`) flag set, or a `TypeError` is thrown. Matches the behavior of the bultin [`String.property.replaceAll`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/replaceAll).
+If `substitution` is a regex, then it must have the global (`g`) flag set, or a `TypeError` is thrown. Matches the behavior of the builtin [`String.property.replaceAll`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/replaceAll).
 
 ### s.remove( start, end )
 

package-lock.json

@@ -33,6 +33,7 @@
     "changelog": "conventional-changelog -p angular -i CHANGELOG.md -s",
     "format": "prettier --single-quote --print-width 100 --use-tabs --write src/*.js src/**/*.js",
     "lint": "eslint src test && publint",
+    "lint:fix": "eslint src test --fix",
     "prepare": "npm run build",
     "prepublishOnly": "npm run lint && rm -rf dist && npm test",
     "release": "bumpp -x \"npm run changelog\" --all --commit --tag --push && npm publish",

package.json

@@ -797,21 +797,29 @@ export default class MagicString {
 		if (searchValue.global) {
 			const matches = matchAll(searchValue, this.original);
 			matches.forEach((match) => {
-				if (match.index != null)
+				if (match.index != null) {
+					const replacement = getReplacement(match, this.original);
+					if (replacement !== match[0]) {
+						this.overwrite(
+							match.index,
+							match.index + match[0].length,
+							replacement
+						);
+					}
+				}
+			});
+		} else {
+			const match = this.original.match(searchValue);
+			if (match && match.index != null) {
+				const replacement = getReplacement(match, this.original);
+				if (replacement !== match[0]) {
 					this.overwrite(
 						match.index,
 						match.index + match[0].length,
-						getReplacement(match, this.original),
+						replacement
 					);
-			});
-		} else {
-			const match = this.original.match(searchValue);
-			if (match && match.index != null)
-				this.overwrite(
-					match.index,
-					match.index + match[0].length,
-					getReplacement(match, this.original),
-				);
+				}
+			}
 		}
 		return this;
 	}
@@ -843,7 +851,9 @@ export default class MagicString {
 			index !== -1;
 			index = original.indexOf(string, index + stringLength)
 		) {
-			this.overwrite(index, index + stringLength, replacement);
+			const previous = original.slice(index, index + stringLength);
+			if (previous !== replacement)
+				this.overwrite(index, index + stringLength, replacement);
 		}
 
 		return this;

src/MagicString.js

@@ -1758,6 +1758,25 @@ describe('MagicString', () => {
 				new MagicString(code).replace(regex, replacer).toString()
 			);
 		});
+
+		it('should ignore non-changed replacements', () => {
+			const code = 'a12bc345#$*%';
+			const matched = [];
+
+			const s = new MagicString(code);
+
+			assert.strictEqual(s.firstChunk, s.lastChunk);
+
+			s.replace(/(\d)/g, (match, $1) => {
+				matched.push($1);
+				return match;
+			});
+
+			assert.strictEqual(s.toString(), code);
+			assert.deepStrictEqual(matched, ['1', '2', '3', '4', '5']);
+
+			assert.strictEqual(s.firstChunk, s.lastChunk);
+		});
 	});
 
 	describe('replaceAll', () => {