@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-dev @babel/runtime-corejs2

or using yarn:

yarn add @babel/runtime-corejs2 --dev

Changelog

v7.15.3 (2021-08-11)

:eyeglasses: Spec Compliance

• babel-helpers, babel-plugin-transform-classes
  • #13571 Derived constructors should not be allowed to return primitives (@dhrubesh)

:bug: Bug Fix

• babel-parser
  • #13659 Fix parse error when using named import "as" with flow parser (@doing-art)
  • #13655 [flow] Fix parsing of arrows in conditional expressions in parentheses (@nicolo-ribaudo)
  • #13645 Disallow <T>(a => b) when parsing Flow (@nicolo-ribaudo)
  • #13657 fix(parser): add attachComment to ParserOptions type (@sosukesuzuki)

:house: Internal

• #13643 Use @babel/eslint-parser/experimental-worker for our own repo (@nicolo-ribaudo)

:running_woman: Performance

• babel-parser
  • #13652 perf: minor tokenizer tweaks (@lightmare)
• babel-register
  • #13654 Reduce stat calls in register (@overlookmotel)