@babel/helpers

What is @babel/helpers?

The @babel/helpers package is part of the Babel toolchain, which is primarily used for converting ECMAScript 2015+ code into a backwards compatible version of JavaScript in current and older browsers or environments. This specific package contains a set of functions that are used by Babel's transform plugins to avoid code duplication across generated output. These helpers are small snippets of code that perform common tasks used by the transformations, such as handling classes, spreading properties, etc.

What are @babel/helpers's main functionalities?

Class handling

This code demonstrates a helper function used by Babel to ensure that a class is only instantiated with the `new` keyword, preventing incorrect usage.

"use strict";\nfunction _classCallCheck(instance, Constructor) { if (!(instance instanceof Constructor)) { throw new TypeError(\"Cannot call a class as a function\"); } }\nvar MyClass = function MyClass() { _classCallCheck(this, MyClass); };

Spread properties

This helper function is used to emulate the behavior of the object spread operator `{...obj}`, allowing properties from one or more source objects to be copied into a new object.

"use strict";\nfunction _extends() { _extends = Object.assign || function (target) { for (var i = 1; i < arguments.length; i++) { var source = arguments[i]; for (var key in source) { if (Object.prototype.hasOwnProperty.call(source, key)) { target[key] = source[key]; } } } return target; }; return _extends.apply(this, arguments); }\nvar obj = _extends({}, sourceObj, { key: 'value' });

Other packages similar to @babel/helpers

core-js

Similar to @babel/helpers, core-js is a modular standard library for JavaScript, including polyfills for ECMAScript up to 2021. While @babel/helpers provides functions to support the transformation process, core-js focuses on polyfilling new JavaScript features for older environments.

regenerator-runtime

This package provides runtime support for generators and async functions, similar to how @babel/helpers supports various syntax transformations. It's often used in conjunction with Babel for projects that use generators or async/await syntax to ensure compatibility with older environments.

README

@babel/helpers

Collection of helper functions used by Babel transforms.

Install

npm install --save-dev @babel/helpers

Usage

Direct:

import * as helpers from '@babel/helpers';
import * as t from '@babel/types';

const typeofHelper = helpers.get('typeof');

t.isExpressionStatement(typeofHelper);
// true

Inside a plugin:

export default {
  visitor: {
    UnaryExpression(path) {
      // The .addHelper function adds, if needed, the helper to the file
      // and returns an expression which references the helper
      const typeofHelper = this.addHelper("typeof");
      t.isExpression(typeofHelper); // true
  }
};

Defining Helpers

NOTE: This package is only meant to be used by the packages inluded in this repository. There is currently no way for third-party plugins to define an helper.

Helpers are defined in the src/helpers.js file, and they must be valid modules which follow these guidelines:

• They must have a default export, which is their entry-point.
• They can import other helpers, exclusively by using default imports.
• They can't have named exports.

helpers.customHelper = defineHelper(`
  import dep from "dependency";
  const foo = 2;
  export default function getFooTimesDepPlusX(x) {
    return foo * dep() + x;
  }
`);