如何安装 babel-polyfill 库？

Question

I just started to use Babel to compile my ES6 javascript code into ES5. When I start to use Promises it looks like it's not working. The Babel website states support for promises via polyfills.

Without any luck, I tried to add:

require("babel/polyfill");

or

import * as p from "babel/polyfill";

With that I'll get the following error on my app bootstrapping:

Cannot find module 'babel/polyfill'

I searched for the module but it seems I'm missing some fundamental thing here. I also tried to add the old and good bluebird NPM but it looks like it's not working.

How to use the polyfills from Babel?

Answer 1

This changed a bit in babel v6.

From the docs:

The polyfill will emulate a full ES6 environment. This polyfill is automatically loaded when using babel-node.

Installation:
$ npm install babel-polyfill

Usage in Node / Browserify / Webpack:
To include the polyfill you need to require it at the top of the entry point to your application.
require("babel-polyfill");

Usage in Browser:
Available from the dist/polyfill.js file within a babel-polyfill npm release. This needs to be included before all your compiled Babel code. You can either prepend it to your compiled code or include it in a <script> before it.

NOTE: Do not require this via browserify etc, use babel-polyfill .

Answer 2

The Babel docs describe this pretty concisely:

Babel includes a polyfill that includes a custom regenerator runtime and core.js.

This will emulate a full ES6 environment. This polyfill is automatically loaded when using babel-node and babel/register.

Make sure you require it at the entry-point to your application, before anything else is called. If you're using a tool like webpack, that becomes pretty simple (you can tell webpack to include it in the bundle).

If you're using a tool like gulp-babel or babel-loader , you need to also install the babel package itself to use the polyfill.

Also note that for modules that affect the global scope (polyfills and the like), you can use a terse import to avoid having unused variables in your module:

import 'babel/polyfill';

Answer 3

For Babel version 7, if your are using @babel/preset-env, to include polyfill all you have to do is add a flag 'useBuiltIns' with the value of 'usage' in your babel configuration. There is no need to require or import polyfill at the entry point of your App.

With this flag specified, babel@7 will optimize and only include the polyfills you needs.

To use this flag, after installation:

npm install --save-dev  @babel/core @babel/cli @babel/preset-env
npm install --save @babel/polyfill

Simply add the flag:

useBuiltIns: "usage" 

to your babel configuration file called "babel.config.js" (also new to Babel@7), under the "@babel/env" section:

// file: babel.config.js

module.exports = () => {
   const presets = [
      [
         "@babel/env", 
         { 
             targets: { /* your targeted browser */ },
             useBuiltIns: "usage"  // <-----------------*** add this
         }
      ]
   ];

   return { presets };
};

Reference:

• usage#polyfill
• babel-polyfill#usage-in-node-browserify-webpack
• babel-preset-env#usebuiltins

---

Update Aug 2019:

With the release of Babel 7.4.0 (March 19, 2019) @babel/polyfill is deprecated. Instead of installing @babe/polyfill, you will install core-js:

npm install --save core-js@3

A new entry corejs is added to your babel.config.js

// file: babel.config.js

module.exports = () => {
   const presets = [
      [
         "@babel/env", 
         { 
             targets: { /* your targeted browser */ },
             useBuiltIns: "usage",
             corejs: 3  // <----- specify version of corejs used
         }
      ]
   ];

   return { presets };
};

see example: https://github.com/ApolloTang/stackoverflow-eg--babel-v7.4.0-polyfill-w-core-v3

Reference:

• 7.4.0 Released: core-js 3, static private methods and partial application
• core-js@3, babel and a look into the future

Answer 4

If your package.json looks something like the following:

  ...
  "devDependencies": {
    "babel": "^6.5.2",
    "babel-eslint": "^6.0.4",
    "babel-polyfill": "^6.8.0",
    "babel-preset-es2015": "^6.6.0",
    "babelify": "^7.3.0",
  ...

And you get the Cannot find module 'babel/polyfill' error message, then you probably just need to change your import statement FROM:

import "babel/polyfill";

TO:

import "babel-polyfill";

And make sure it comes before any other import statement (not necessarily at the entry point of your application).

Reference: https://babeljs.io/docs/usage/polyfill/

Answer 5

First off, the obvious answer that no one has provided, you need to install Babel into your application:

npm install babel --save

(or babel-core if you instead want to require('babel-core/polyfill') ).

Aside from that, I have a grunt task to transpile my es6 and jsx as a build step (ie I don't want to use babel/register , which is why I am trying to use babel/polyfill directly in the first place), so I'd like to put more emphasis on this part of @ssube's answer:

Make sure you require it at the entry-point to your application, before anything else is called

I ran into some weird issue where I was trying to require babel/polyfill from some shared environment startup file and I got the error the user referenced - I think it might have had something to do with how babel orders imports versus requires but I'm unable to reproduce now. Anyway, moving import 'babel/polyfill' as the first line in both my client and server startup scripts fixed the problem.

Note that if you instead want to use require('babel/polyfill') I would make sure all your other module loader statements are also requires and not use imports - avoid mixing the two. In other words, if you have any import statements in your startup script, make import babel/polyfill the first line in your script rather than require('babel/polyfill') .

Answer 6

babel-polyfill allows you to use the full set of ES6 features beyond syntax changes. This includes features such as new built-in objects like Promises and WeakMap, as well as new static methods like Array.from or Object.assign.

Without babel-polyfill, babel only allows you to use features like arrow functions, destructuring, default arguments, and other syntax-specific features introduced in ES6.

https://www.quora.com/What-does-babel-polyfill-do

https://hackernoon.com/polyfills-everything-you-ever-wanted-to-know-or-maybe-a-bit-less-7c8de164e423

Answer 7

Like Babel says in the docs , for Babel > 7.4.0 the module @babel/polyfill is deprecated , so it's recommended to use directly core-js and regenerator-runtime libraries that before were included in @babel/polyfill.

So this worked for me:

npm install --save core-js@3.6.5
npm install regenerator-runtime

then add to the very top of your initial js file:

import 'core-js/stable';
import 'regenerator-runtime/runtime';