@babel/runtime-corejs2

What is @babel/runtime-corejs2?

@babel/runtime-corejs2 is a library that provides a runtime for Babel that includes polyfills for ECMAScript features using core-js@2. It helps to avoid code duplication and reduce the size of the compiled code by providing helpers and polyfills as separate modules.

What are @babel/runtime-corejs2's main functionalities?

Polyfilling ECMAScript features

This feature allows you to polyfill ECMAScript features like Map and Set, ensuring compatibility with older environments that do not support these features natively.

import 'core-js/es6/map';
import 'core-js/es6/set';

const map = new Map();
const set = new Set();

Helper functions

This feature provides helper functions like classCallCheck to ensure that classes are instantiated correctly, which is useful for maintaining compatibility with older JavaScript environments.

import _classCallCheck from '@babel/runtime-corejs2/helpers/classCallCheck';

class MyClass {
  constructor() {
    _classCallCheck(this, MyClass);
  }
}

Async/Await support

This feature provides support for async/await syntax by transforming it into generator functions, which are compatible with older JavaScript environments.

import _asyncToGenerator from '@babel/runtime-corejs2/helpers/asyncToGenerator';
import regeneratorRuntime from 'regenerator-runtime';

const asyncFunction = _asyncToGenerator(function* () {
  const result = yield fetch('https://api.example.com/data');
  return result.json();
});

asyncFunction().then(data => console.log(data));

Other packages similar to @babel/runtime-corejs2

@babel/runtime

@babel/runtime is a similar package that provides the same runtime helpers and polyfills but uses core-js@3 instead of core-js@2. It is more up-to-date and recommended for new projects.

core-js

core-js is a modular standard library for JavaScript that includes polyfills for ECMAScript features. It can be used directly to polyfill features without relying on Babel's runtime.

regenerator-runtime

regenerator-runtime is a runtime library for transforming generator functions and async/await syntax. It is often used in conjunction with Babel to provide support for these features in older environments.

README

@babel/runtime-corejs2

babel's modular runtime helpers with core-js@2 polyfilling

See our website @babel/runtime-corejs2 for more information.

Install

Using npm:

npm install --save @babel/runtime-corejs2

or using yarn:

yarn add @babel/runtime-corejs2

Changelog

v7.27.0 (2025-03-24)

:eyeglasses: Spec Compliance

• babel-generator, babel-parser
  • #16977 Default importAttributesKeyword to with (@JLHwung)

:rocket: New Feature

• babel-helper-create-class-features-plugin, babel-traverse, babel-types
  • #17169 Allow traverseFast to exit early (@liuxingbaoyu)
• babel-parser, babel-types
  • #17110 Add ImportAttributes to Standardized and move its parser test fixtures (@JLHwung)
• babel-generator
  • #17100 fix(babel-generator): add named export of generate function (@vovkasm)
• babel-parser, babel-template
  • #17149 Add allowYieldOutsideFunction to parser (@liuxingbaoyu)
• babel-plugin-transform-typescript, babel-traverse
  • #17102 feat: Add upToScope parameter to hasBinding (@liuxingbaoyu)
• babel-parser
  • #17082 Support ESTree AccessorProperty (@JLHwung)
• babel-types
  • #17162 feat(babel-types): Add support for BigInt literal conversion in valueToNode (@ishchhabra)

:bug: Bug Fix

• babel-helper-create-class-features-plugin, babel-plugin-transform-class-properties
  • #16816 fix: Class reference in type throws error (@liuxingbaoyu)
• babel-traverse
  • #17170 fix: Reset child scopes when scope.crawl() (@liuxingbaoyu)
• babel-helpers, babel-preset-typescript, babel-runtime-corejs2, babel-runtime-corejs3, babel-runtime
  • #17118 Fix: align behaviour to tsc rewriteRelativeImportExtensions (@JLHwung)
• babel-cli
  • #17182 fix: @babel/cli generates duplicate inline source maps (@liuxingbaoyu)
• babel-plugin-transform-named-capturing-groups-regex, babel-types
  • #17175 Generate computed proto key (@JLHwung)

:running_woman: Performance

• babel-types
  • #16870 perf: Improve builders of @babel/types (@liuxingbaoyu)
• babel-helper-create-regexp-features-plugin
  • #17176 fix: improve duplicate named groups check (@JLHwung)