@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

v7.25.0 (2024-07-26)

:eyeglasses: Spec Compliance

• babel-helpers, babel-plugin-proposal-explicit-resource-management, babel-runtime-corejs3
  • #16537 await using normative updates (@JLHwung)
• babel-plugin-transform-typescript
  • #16602 Ensure enum members syntactically determinable to be strings do not get reverse mappings (@liuxingbaoyu)

:rocket: New Feature

• babel-helper-create-class-features-plugin, babel-helper-function-name, babel-helper-plugin-utils, babel-helper-wrap-function, babel-plugin-bugfix-safari-class-field-initializer-scope, babel-plugin-bugfix-safari-id-destructuring-collision-in-function-expression, babel-plugin-transform-classes, babel-plugin-transform-function-name, babel-preset-env, babel-traverse, babel-types
  • #16658 Move ensureFunctionName to NodePath.prototype (@nicolo-ribaudo)
• babel-helper-hoist-variables, babel-helper-plugin-utils, babel-plugin-proposal-async-do-expressions, babel-plugin-transform-modules-systemjs, babel-traverse
  • #16644 Move hoistVariables to Scope.prototype (@nicolo-ribaudo)
• babel-helper-create-class-features-plugin, babel-helper-module-transforms, babel-helper-plugin-utils, babel-helper-split-export-declaration, babel-plugin-transform-classes, babel-traverse, babel-types
  • #16645 Move splitExportDeclaration to NodePath.prototype (@nicolo-ribaudo)
• babel-helper-create-class-features-plugin, babel-helper-environment-visitor, babel-helper-module-transforms, babel-helper-plugin-utils, babel-helper-remap-async-to-generator, babel-helper-replace-supers, babel-plugin-bugfix-firefox-class-in-computed-class-key, babel-plugin-bugfix-v8-static-class-fields-redefine-readonly, babel-plugin-transform-async-generator-functions, babel-plugin-transform-classes, babel-traverse
  • #16649 Move environment-visitor helper into @babel/traverse (@nicolo-ribaudo)
• babel-core, babel-parser
  • #16480 Expose wether a module has TLA or not as .extra.async (@nicolo-ribaudo)
• babel-compat-data, babel-plugin-bugfix-safari-class-field-initializer-scope, babel-preset-env
  • #16569 Introduce bugfix-safari-class-field-initializer-scope (@davidtaylorhq)
• babel-plugin-transform-block-scoping, babel-traverse, babel-types
  • #16551 Add NodePath#getAssignmentIdentifiers (@JLHwung)
• babel-helper-import-to-platform-api, babel-plugin-proposal-json-modules
  • #16579 Add uncheckedRequire option for JSON imports to CJS (@nicolo-ribaudo)
• babel-helper-transform-fixture-test-runner, babel-node
  • #16642 Allow using custom config in babel-node --eval (@slatereax)
• babel-compat-data, babel-helper-create-regexp-features-plugin, babel-plugin-proposal-duplicate-named-capturing-groups-regex, babel-plugin-transform-duplicate-named-capturing-groups-regex, babel-preset-env, babel-standalone
  • #16445 Add duplicate-named-capturing-groups-regex to preset-env (@JLHwung)

:bug: Bug Fix

• babel-generator
  • #16678 Print parens around as expressions on the LHS (@nicolo-ribaudo)
• babel-template, babel-types
  • #15286 fix: Props are lost when the template replaces the node (@liuxingbaoyu)

:house: Internal

• Other
  • #16674 bump gulp to 5 (@JLHwung)
• babel-generator
  • #16651 Simplify the printing logic for ( before ambiguous tokens (@nicolo-ribaudo)
• babel-helper-function-name, babel-plugin-transform-arrow-functions, babel-plugin-transform-function-name, babel-preset-env, babel-traverse
  • #16652 Simplify helper-function-name logic (@nicolo-ribaudo)

:running_woman: Performance

• babel-parser, babel-plugin-proposal-pipeline-operator
  • #16461 Some minor parser performance improvements for ts (@liuxingbaoyu)

:microscope: Output optimization

• babel-plugin-transform-classes
  • #16670 Reduce redundant assertThisInitialized (@liuxingbaoyu)
• babel-helper-create-class-features-plugin, babel-helper-replace-supers, babel-helpers, babel-plugin-proposal-decorators, babel-plugin-transform-class-properties, babel-plugin-transform-classes, babel-plugin-transform-exponentiation-operator, babel-plugin-transform-object-super, babel-plugin-transform-private-methods, babel-runtime-corejs2, babel-runtime-corejs3, babel-runtime
  • #16374 Improve super.x output (@liuxingbaoyu)
• babel-plugin-transform-class-properties, babel-plugin-transform-classes
  • #16656 Simplify output for anonymous classes with no methods (@nicolo-ribaudo)