babel-plugin-polyfill-corejs2

0.4.17 verified Sat Apr 25 auth: no javascript maintenance

Babel plugin that automatically injects imports for core-js@2 polyfills based on language features used in the code. Current stable version is 0.4.17, released as part of the Babel polyfills project. Unlike manual core-js imports or @babel/polyfill, this plugin offers fine-grained control via methods like 'usage-global' (per-file polyfill injection into global scope), 'usage-pure' (pure expressions without side effects), and 'entry-global' (replaces core-js import entries). Requires @babel/core peer dependency. Development is focused on core-js@2 compatibility; for core-js@3 use babel-plugin-polyfill-corejs3.

Common errors

error Cannot find module 'core-js' ↓

cause core-js@2 not installed as a dependency.

fix

Install core-js@2: npm install core-js@2

error Error: [BABEL] unknown: You gave us a visitor for the node type "ImportDeclaration" but it's not a valid type ↓

cause Using incompatible version of @babel/core (older than 7.4.0).

fix

Update @babel/core to ^7.4.0.

error ReferenceError: regeneratorRuntime is not defined ↓

cause Plugin does not include regenerator-runtime; needed for async/await.

fix

Add @babel/plugin-transform-regenerator or manually import regenerator-runtime.

error The 'entry-global' method did not inject any polyfills ↓

cause No import statement for core-js found in the file; method expects an explicit import like 'import "core-js"'.

fix

Add 'import "core-js"' at the entry point of your application, or switch to 'usage-global' method.

Warnings

deprecated core-js@2 is deprecated; consider migrating to core-js@3 and babel-plugin-polyfill-corejs3. ↓

fix Replace this plugin with babel-plugin-polyfill-corejs3 and core-js@3.

gotcha The plugin does not automatically install core-js; you must add core-js@2 as a dependency in your package.json. ↓

fix Run 'npm install core-js@2' or equivalent.

breaking From version 0.2.0, the plugin replaces global core-js imports only when 'entry-global' method is used; prior versions defaulted differently. ↓

fix Update to 0.4.x and explicitly set method to 'entry-global' if you previously relied on global injection.

gotcha Using 'usage-pure' method may cause polyfill duplication if multiple files use the same feature. Use 'usage-global' for single global polyfills. ↓

fix Select method carefully: 'usage-pure' for library development, 'usage-global' for applications.

deprecated The 'entry-global' method replaces core-js entries but does not handle proposals; use @babel/plugin-proposal-* for proposals. ↓

fix Add corresponding proposal plugins (e.g., @babel/plugin-proposal-optional-chaining) alongside this plugin.

Install

npm install babel-plugin-polyfill-corejs2

yarn add babel-plugin-polyfill-corejs2

pnpm add babel-plugin-polyfill-corejs2

Imports

default
wrong
```
const plugin = require('babel-plugin-polyfill-corejs2'); // Works in CJS but not recommended for ESM-only projects
```
correct
```
import plugin from 'babel-plugin-polyfill-corejs2'; // In Babel config file (ESM)
```
This is a Babel plugin, not typically imported directly; instead listed in .babelrc or babel.config.js as 'polyfill-corejs2' string or [require('babel-plugin-polyfill-corejs2'), options] in JS config.

Method options

wrong

// Using invalid method: { plugins: [['polyfill-corejs2', { method: 'global' }]] }

correct

// In Babel config: { plugins: [['polyfill-corejs2', { method: 'usage-global' }]] }

Valid methods are 'usage-global', 'usage-pure', and 'entry-global'. Do not omit method or use a typo.

Programmatic usage

wrong

const babel = require('@babel/core');
const plugin = require('babel-plugin-polyfill-corejs2');
babel.transform(code, { plugins: [plugin] }); // Missing options or incorrect method

correct

import babel from '@babel/core';
import plugin from 'babel-plugin-polyfill-corejs2';
babel.transformSync(code, { plugins: [[plugin, { method: 'usage-pure' }]] });

Must pass plugin options as an array; omitting options may default to 'usage-global' but explicit is safer.

Quickstart

Install the plugin and core-js@2 peer dependency. Note: core-js@2 is a required runtime dependency for polyfills.

npm install --save-dev babel-plugin-polyfill-corejs2 core-js@2 @babel/core