@babel/preset-env

@babel/preset-env 是一個“聰明”的預設（preset），它能讓你使用最新的 JavaScript 語法而無需操心對目標環(huán)境所支持的語法設置相應的語法轉(zhuǎn)換插件（以及可選的 polyfills）。這樣能讓你的工作更輕松，也能讓打出來的 JavaScript 包更?。?/p>

• 安裝
• 工作原理
• 與 Browserslist 集成
• 參數(shù)

安裝?

• npm
• Yarn
• pnpm

pnpm add --save-dev @babel/preset-env

工作原理?

@babel/preset-env 是構(gòu)建其它的優(yōu)秀開源項目之上的，例如 browserslist、compat-table 以及 electron-to-chromium 等。

We leverage these data sources to maintain mappings of which version of our supported target environments gained support of a JavaScript syntax or browser feature, as well as a mapping of those syntaxes and features to Babel transform plugins and core-js polyfills.

注意： @babel/preset-env 不包含任何未進入 Stage 3 階段的 JavaScript 語法提案，因為在 TC39 的流程中，未進入 Stage 3 階段的提案是不會被任何瀏覽器所實現(xiàn)的。如果確有需要，請手動設置。通過設置 shippedProposals 參數(shù)可以包含進入 Stage 3 階段并且已經(jīng)被部分瀏覽器實現(xiàn)的提案。

@babel/preset-env takes any target environments you've specified and checks them against its mappings to compile a list of plugins and passes it to Babel.

與 Browserslist 集成?

對于基于瀏覽器或 Electron 的項目，我們建議使用 .browserslistrc 文件來指定目標環(huán)境。你可能已經(jīng)有這個配置文件了，因為 JavaScript 生態(tài)中的其它工具也支持該配置文件，例如 autoprefixer、 stylelint、eslint-plugin-compat 等等。

默認情況下，@babel/preset-env 將使用 browserslist 配置文件， 除非 設置了 targets 或 ignoreBrowserslistConfig 參數(shù)。

請注意，如果t if you are relying on browserslist's defaults query (either explicitly or by having no browserslist config), you will want to check out the No targets section for information on preset-env's behavior.

例如，to only include polyfills and code transforms needed for users whose browsers have >0.25% market share (ignoring browsers without security updates like IE 10 and BlackBerry):

babel.config.json

{
  "presets": [
    [
      "@babel/preset-env",
      {
        "useBuiltIns": "entry",
        "corejs": "3.22"
      }
    ]
  ]
}

.browserslistrc

> 0.25%
not dead

或者

package.json

{ "browserslist": "> 0.25%, not dead" }

請注意，從 v7.4.5 版本開始，browserslist 查詢 is resolved with mobileToDesktop: true. 例如，如果 if you want to create a snapshot of a query run npx browserslist --mobile-to-desktop ">0.25%, not dead".

參數(shù)?

For more information on setting options for a preset, refer to the preset options documentation.

targets?

string | Array<string> | { [string]: string }, defaults to the top-level targets option if no browserslist-related option is specified in @babel/preset-env's docs, otherwise to {}.

For usage, refer to the targets option documentation.

bugfixes?

boolean, defaults to false.

Added in: v7.9.0

Note: These optimizations will be enabled by default in Babel 8

By default, @babel/preset-env (and Babel plugins in general) grouped ECMAScript syntax features into collections of closely related smaller features. These groups can be large and include a lot of edge cases, for example "function arguments" includes destructured, default and rest parameters. From this grouping information, Babel enables or disables each group based on the browser support target you specify to @babel/preset-env’s targets option.

When this option is enabled, @babel/preset-env tries to compile the broken syntax to the closest non-broken modern syntax supported by your target browsers. Depending on your targets and on how many modern syntax you are using, this can lead to a significant size reduction in the compiled app. This option merges the features of @babel/preset-modules without having to use another preset.

spec?

boolean, defaults to false.

Enable more spec compliant, but potentially slower, transformations for any plugins in this preset that support them.

loose?

boolean, defaults to false.

Enable "loose" transformations for any plugins in this preset that allow them.

?? Consider migrating to the top level assumptions available since Babel 7.13.

modules?

"amd" | "umd" | "systemjs" | "commonjs" | "cjs" | "auto" | false, defaults to "auto".

Enable transformation of ES module syntax to another module type. Note that cjs is just an alias for commonjs.

Setting this to false will preserve ES modules. Use this only if you intend to ship native ES Modules to browsers. If you are using a bundler with Babel, the default modules: "auto" is always preferred.

modules: "auto"?

By default @babel/preset-env uses caller data to determine whether ES modules and module features (e.g. import()) should be transformed. Generally caller data will be specified in the bundler plugins (e.g. babel-loader, @rollup/plugin-babel) and thus it is not recommended to pass caller data yourself -- The passed caller may overwrite the one from bundler plugins and in the future you may get suboptimal results if bundlers supports new module features.

debug?

boolean, defaults to false.

Outputs to console.log the polyfills and transform plugins enabled by preset-env and, if applicable, which one of your targets that needed it.

include?

Array<string|RegExp>, defaults to [].

An array of plugins to always include.

Valid options include any:

• Babel plugins - both full and shorthand names are supported, for example the following are functionally equivalent:@babel/plugin-transform-spread@babel/transform-spreadbabel-transform-spreadtransform-spread
• Built-ins (both for core-js@2 and core-js@3, such as es.map, es.set, or es.object.assign.

Plugin names can be fully or partially specified (or using RegExp).

Acceptable inputs:

• Full name (string): "es.math.sign"
• Partial name (string): "es.math.*" (resolves to all plugins with es.math prefix)
• RegExp Object: /^transform-.*$/ or new RegExp("^transform-modules-.*")

Note that the above . is the RegExp equivalent to match any character, and not the actual '.' character. Also note that to match any character .* is used in RegExp as opposed to * in glob format.

This option is useful if there is a bug in a native implementation, or a combination of a non-supported feature + a supported one doesn't work.

For example, Node 4 supports native classes but not spread. If super is used with a spread argument, then the @babel/plugin-transform-classes transform needs to be included, as it is not possible to transpile a spread with super otherwise.

NOTE: The include and exclude options only work with the plugins included with this preset; so, for example, including @babel/plugin-proposal-do-expressions or excluding @babel/plugin-proposal-function-bind will throw errors. To use a plugin not included with this preset, add them to your "plugins" directly.

exclude?

Array<string|RegExp>, defaults to [].

An array of plugins to always exclude/remove.

The possible options are the same as the include option.

This option is useful for excluding a transform like @babel/plugin-transform-regenerator if you don't use generators and don't want to include regeneratorRuntime (when using useBuiltIns) or for using another plugin like  fast-async instead of Babel's async-to-gen.

useBuiltIns?

"usage" | "entry" | false, defaults to false.

This option configures how @babel/preset-env handles polyfills.

When either the usage or entry options are used, @babel/preset-env will add direct references to core-js modules as bare imports (or requires). This means core-js will be resolved relative to the file itself and needs to be accessible.

Since @babel/polyfill was deprecated in 7.4.0, we recommend directly adding core-js and setting the version via the corejs option.

• npm
• Yarn
• pnpm

pnpm add core-js@3

# or

pnpm add core-js@2

useBuiltIns: 'entry'?

NOTE: Only use import "core-js"; once in your whole app. If you are using @babel/polyfill, it already includes core-js: importing it twice will throw an error. Multiple imports or requires of those packages might cause global collisions and other issues that are hard to trace. We recommend creating a single entry file that only contains the import statements.

This option enables a new plugin that replaces the import "core-js/stable"; and require("core-js"); statements with individual imports to different core-js entry points based on environment.

In

JavaScript

import "core-js";

Out (different based on environment)

JavaScript

import "core-js/modules/es.string.pad-start";
import "core-js/modules/es.string.pad-end";

Importing "core-js" loads polyfills for every possible ECMAScript feature: what if you know that you only need some of them? When using core-js@3, @babel/preset-env is able to optimize every single core-js entrypoint and their combinations. For example, you might want to only polyfill array methods and new Math proposals:

In

JavaScript

import "core-js/es/array";
import "core-js/proposals/math-extensions";

Out (different based on environment)

JavaScript

import "core-js/modules/es.array.unscopables.flat";
import "core-js/modules/es.array.unscopables.flat-map";
import "core-js/modules/esnext.math.clamp";
import "core-js/modules/esnext.math.deg-per-rad";
import "core-js/modules/esnext.math.degrees";
import "core-js/modules/esnext.math.fscale";
import "core-js/modules/esnext.math.rad-per-deg";
import "core-js/modules/esnext.math.radians";
import "core-js/modules/esnext.math.scale";

You can read core-js's documentation for more information about the different entry points.

NOTE: When using core-js@2 (either explicitly using the corejs: "2" option or implicitly), @babel/preset-env will also transform imports and requires of @babel/polyfill. This behavior is deprecated because it isn't possible to use @babel/polyfill with different core-js versions.

useBuiltIns: 'usage'?

Adds specific imports for polyfills when they are used in each file. We take advantage of the fact that a bundler will load the same polyfill only once.

In

a.js

var a = new Promise();

b.js

var b = new Map();

Out (if environment doesn't support it)

a.js

import "core-js/modules/es.promise";
var a = new Promise();

b.js

import "core-js/modules/es.map";
var b = new Map();

Out (if environment supports it)

a.js

var a = new Promise();

b.js

var b = new Map();

useBuiltIns: false?

Don't add polyfills automatically per file, and don't transform import "core-js" or import "@babel/polyfill" to individual polyfills.

corejs?

Added in: v7.4.0

string or { version: string, proposals: boolean }, defaults to "2.0". The version string can be any supported core-js versions. For example, "3.8" or "2.0".

This option only has an effect when used alongside useBuiltIns: usage or useBuiltIns: entry, and ensures @babel/preset-env injects the polyfills supported by your core-js version. It is recommended to specify the minor version otherwise "3" will be interpreted as "3.0" which may not include polyfills for the latest features.

By default, only polyfills for stable ECMAScript features are injected: if you want to polyfill proposals, you have three different options:

• when using useBuiltIns: "entry", you can directly import a proposal polyfill: import "core-js/proposals/string-replace-all".
• when using useBuiltIns: "usage" you have two different alternatives:set the shippedProposals option to true. This will enable polyfills and transforms for proposal which have already been shipped in browsers for a while.use corejs: { version: "3.8", proposals: true }. This will enable polyfilling of every proposal supported by core-js@3.8.

forceAllTransforms?

boolean, defaults to false.

NOTE: targets.uglify is deprecated and will be removed in the next major in favor of this.

By default, this preset will run all the transforms needed for the targeted environment(s). Enable this option if you want to force running all transforms, which is useful if the output will be run through UglifyJS or an environment that only supports ES5.

NOTE: If you require an alternative minifier which does support ES6 syntax, we recommend Terser.

configPath?

string, defaults to process.cwd()

The starting point where the config search for browserslist will start, and ascend to the system root until found.

ignoreBrowserslistConfig?

boolean, defaults to false

Toggles whether or not browserslist config sources are used, which includes searching for any browserslist files or referencing the browserslist key inside package.json. This is useful for projects that use a browserslist config for files that won't be compiled with Babel.

browserslistEnv?

Added in: v7.10.0 string, defaults to undefined

The Browserslist environment to use.

shippedProposals?

boolean, defaults to false

Toggles enabling support for builtin/feature proposals that have shipped in browsers. If your target environments have native support for a feature proposal, its matching parser syntax plugin is enabled instead of performing any transform. Note that this does not enable the same transformations as @babel/preset-stage-3, since proposals can continue to change before landing in browsers.

The following are currently supported:

Builtins injected when using useBuiltIns: "usage"

• esnext.global-this (only supported by core-js@3)
• esnext.string.match-all (only supported by core-js@3)

Features

• Class static block
• Import assertions (parsing only)
• Private field brand checks

Materialized Features These features were behind shippedProposals flag in older Babel versions. They are now generally available.

• class properties
• numeric separator
• private methods

You can read more about configuring preset options here

Caveats?

Ineffective browserslist queries?

While op_mini all is a valid browserslist query, preset-env currently ignores it due to lack of support data for Opera Mini.