@babel/polyfill

---

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

This will emulate a full ES2015+ environment (no < Stage 4 proposals) and is intended to be used in an application rather than a library/tool. (this polyfill is automatically loaded when using babel-node).

This means you can use new built-ins like Promise or WeakMap, static methods like Array.from or Object.assign, instance methods like Array.prototype.includes, and generator functions (provided you use the regenerator plugin). The polyfill adds to the global scope as well as native prototypes like String in order to do this.

Installation

 sh
npm install --save @babel/polyfill

Because this is a polyfill (which will run before your source code), we need it to be a dependency, not a devDependency

Size

The polyfill is provided as a convenience but you should use it with code>@babel/preset-env</code and the useBuiltIns option so that it doesn’t include the whole polyfill which isn’t always needed. Otherwise, we would recommend you import the individual polyfills manually.

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TC39 Proposals

If you need to use a proposal that is not Stage 4, code>@babel/polyfill</code will not automatically import those for you. You will have to import those from another polyfill like core-js individually. We may work towards including this as separate files in code>@babel/polyfill</code soon.

Usage in Node / Browserify / Webpack

To include the polyfill you need to require it at the top of the entry point to your application.

Make sure it is called before all other code/require statements!

 js
require("@babel/polyfill");

If you are using ES6’s import syntax in your application’s entry point, you should instead import the polyfill at the top of the entry point to ensure the polyfills are loaded first:

 js
import "@babel/polyfill";

With webpack, there are multiple ways to include the polyfills:

• When used alongside @babel/preset-env,
  • If useBuiltIns: 'usage' is specified in .babelrc then do not include @babel/polyfill in either webpack.config.js entry array nor source. Note, @babel/polyfill still needs to be installed.
  • If useBuiltIns: 'entry' is specified in .babelrc then include @babel/polyfill at the top of the entry point to your application via require or import as discussed above.
  • If useBuiltIns key is not specified or it is explicitly set with useBuiltIns: false in your .babelrc, add @babel/polyfill directly to the entry array in your webpack.config.js.

 js
module.exports = {
  entry: ["@babel/polyfill", "./app/js"],
};

• If @babel/preset-env is not used then add @babel/polyfill to webpack entry array as discussed above. It can still be added at the top of the entry point to application via import or require, but this is not recommended.

We do not recommend that you import the whole polyfill directly: either try the useBuiltIns options or import only the polyfills you need manually (either from this package or somewhere else).

Usage in Browser

Available from the dist/polyfill.js file within a code>@babel/polyfill</code 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 code>@babel/polyfill</code.

Details

If you are looking for something that won’t modify globals to be used in a tool/library, checkout the transform-runtime plugin. This means you won’t be able to use the instance methods mentioned above like Array.prototype.includes.

Note: Depending on what ES2015 methods you actually use, you may not need to use code>@babel/polyfill</code or the runtime plugin. You may want to only load the specific polyfills you are using (like Object.assign) or just document that the environment the library is being loaded in should include certain polyfills.

← clitransform-runtime →

来源：Js中文网 – 前端进阶资源教程
链接：https://www.javascriptc.com/docs/babel-manual/babel-polyfill