call swc only when required

Author: zloirock

packages/core-js-builder/config.mjs

@@ -1,10 +1,10 @@
 const version = '4.0.0-alpha.0';
 
 /* eslint-disable prefer-template -- for better formatting */
-export default '/**\n' +
-               ' * core-js ' + version + '\n' +
-               ' * © 2013–2025 Denis Pushkarev (zloirock.ru), 2025–2026 CoreJS Company (core-js.io). All rights reserved.\n' +
-               ' * license: https://github.com/zloirock/core-js/blob/v' + version + '/LICENSE\n' +
-               ' * source: https://github.com/zloirock/core-js\n' +
-               ' */';
+export const banner '/**\n' +
+                    ' * core-js ' + version + '\n' +
+                    ' * © 2013–2025 Denis Pushkarev (zloirock.ru), 2025–2026 CoreJS Company (core-js.io). All rights reserved.\n' +
+                    ' * license: https://github.com/zloirock/core-js/blob/v' + version + '/LICENSE\n' +
+                    ' * source: https://github.com/zloirock/core-js\n' +
+                    ' */';
 /* eslint-enable prefer-template -- for better formatting */

packages/core-js-builder/index.mjs

@@ -6,7 +6,7 @@ import { styleText } from 'node:util';
 import { build } from 'rolldown';
 import { transform } from '@swc/core';
 import compat from '@core-js/compat/compat.js';
-import banner from './config.mjs';
+import { banner } from './config.mjs';
 
 function normalizeSummary(unit = {}) {
   let size, modules;
@@ -81,15 +81,22 @@ export default async function ({
         await rm(tempFile, { force: true });
       }
 
+      const swcOptions = {};
+
       // rolldown helpers / wrappers contain es2015 syntax
-      const swcOptions = {
+      let syntax = ['arrow-functions', 'shorthand-properties'];
+
+      if (targets) {
+        syntax = compat({ targets, modules: syntax, __external: true }).list;
+      }
+
+      const swcTransforms = syntax.map(it => `transform-${ it }`);
+
+      if (swcTransforms.length) Object.assign(swcOptions, {
         env: {
-          include: [
-            'transform-arrow-functions',
-            'transform-shorthand-properties',
-          ],
+          include: swcTransforms,
         },
-      };
+      });
 
       if (minify) Object.assign(swcOptions, {
         minify: true,
@@ -120,9 +127,11 @@ export default async function ({
         },
       });
 
-      code = (await transform(code, swcOptions)).code;
+      if (swcTransforms.length || minify) {
+        code = (await transform(code, swcOptions)).code;
+      }
 
-      // swc considers output code as a module and drops 'use strict`
+      // swc and rolldown considers output code as a module and drops 'use strict'
       code = `!function () { 'use strict'; ${ code } }();\n`;
     } else {
       code = importModules(list, format);

packages/core-js-compat/compat.js

@@ -1,6 +1,7 @@
 'use strict';
 const { compare, filterOutStabilizedProposals, intersection } = require('./helpers');
 const data = require('./data');
+const externalData = require('./external');
 const entries = require('./entries');
 const getModulesListForTargetVersion = require('./get-modules-list-for-target-version');
 const allModules = require('./modules');
@@ -32,15 +33,15 @@ function normalizeModules(option) {
   return new Set(Array.isArray(option) ? option.flatMap(getModules) : getModules(option));
 }
 
-function checkModule(name, targets) {
+function checkModule(name, targets, external) {
   const result = {
     required: !targets,
     targets: {},
   };
 
   if (!targets) return result;
 
-  const requirements = data[name];
+  const requirements = (external ? externalData : data)[name];
 
   for (const [engine, version] of targets) {
     if (!hasOwn(requirements, engine) || compare(version, '<', requirements[engine])) {
@@ -58,28 +59,31 @@ module.exports = function ({
   targets = null,
   version = null,
   inverse = false,
+  __external = false,
 } = {}) {
-  inverse = !!inverse;
-
   const parsedTargets = targets ? targetsParser(targets) : null;
 
   const result = {
     list: [],
     targets: {},
   };
 
-  exclude = normalizeModules(exclude);
+  if (!__external) {
+    inverse = !!inverse;
+
+    exclude = normalizeModules(exclude);
 
-  modules = modules ? [...normalizeModules(modules)] : actual;
+    modules = modules ? [...normalizeModules(modules)] : actual;
 
-  if (exclude.size) modules = modules.filter(it => !exclude.has(it));
+    if (exclude.size) modules = modules.filter(it => !exclude.has(it));
 
-  modules = intersection(modules, version ? getModulesListForTargetVersion(version) : allModules);
+    modules = intersection(modules, version ? getModulesListForTargetVersion(version) : allModules);
 
-  if (!inverse) modules = filterOutStabilizedProposals(modules);
+    if (!inverse) modules = filterOutStabilizedProposals(modules);
+  }
 
   for (const key of modules) {
-    const check = checkModule(key, parsedTargets);
+    const check = checkModule(key, parsedTargets, __external);
 
     if (check.required ^ inverse) {
       result.list.push(key);

packages/core-js-compat/src/external.mjs

@@ -8,4 +8,22 @@ export default {
     node: '13.2',
     safari: '10.1',
   },
+  'arrow-functions': {
+    chrome: '45',
+    edge: '12',
+    firefox: '22',
+    hermes: '0.7',
+    'react-native': '0.70',
+    rhino: '1.7.13',
+    safari: '10',
+  },
+  'shorthand-properties': {
+    chrome: '43',
+    edge: '12',
+    firefox: '33',
+    hermes: '0.7',
+    'react-native': '0.70',
+    rhino: '1.7.14',
+    safari: '9',
+  },
 };