A Babel preset that can automatically determine the Babel plugins and polyfills you need based on your supported environments.
npm install babel-preset-env --save-dev{
"presets": [
["env", {
"targets": {
"browsers": ["last 2 versions", "safari >= 7"]
}
}]
]
}Check out the many options (especially useBuiltIns to polyfill less)!
Use external data such as compat-table to determine browser support. (We should create PRs there when necessary)
We can periodically run build-data.js which generates plugins.json.
Ref: #7
Currently located at plugin-features.js.
This should be straightforward to do in most cases. There might be cases where plugins should be split up more or certain plugins aren't standalone enough (or impossible to do).
Default behavior without options is the same as
babel-preset-latest.
It won't include stage-x plugins. env will support all plugins in what we consider the latest version of Javascript (by matching what we do in babel-preset-latest).
Ref: #14
If you are targeting IE 8 and Chrome 55 it will include all plugins required by IE 8 since you would need to support both still.
For example, if you are building on Node 4, arrow functions won't be converted, but they will if you build on Node 0.12.
Use browserslist to declare supported environments by performing queries like > 1%, last 2 versions.
Ref: #19
With npm:
npm install --save-dev babel-preset-envOr yarn:
yarn add babel-preset-env --devThe default behavior without options runs all transforms (behaves the same as babel-preset-latest).
{
"presets": ["env"]
}For more information on setting options for a preset, refer to the plugin/preset options documentation.
{ [string]: number }, defaults to {}.
Takes an object of environment versions to support.
Each target environment takes a number (you can also specify a minor versions like node: 6.5)
Example environments: chrome, opera, edge, firefox, safari, ie, ios, android, node, electron.
The data for this is generated by running the build-data script which pulls in data from compat-table.
number | "current" | true
If you want to compile against the current node version, you can specify "node": true or "node": "current", which would be the same as "node": parseFloat(process.versions.node).
Array<string> | string
A query to select browsers (ex: last 2 versions, > 5%) using browserslist.
Note, browsers' results are overridden by explicit items from targets.
number | true
UglifyJS does not currently support any ES6 syntax, so if you are using Uglify to minify your code, targeting later browsers may cause Uglify to throw syntax errors.
To prevent these errors - specify the uglify option, which will enable all plugins and, as a result, fully compile your code to ES5. However, the useBuiltIns option will still work as before, and only include the polyfills that your target(s) need.
NOTE: Uglify has a work-in-progress "Harmony" branch to address the lack of ES6 support, but it is not yet stable. You can follow its progress in UglifyJS2 issue #448. If you require an alternative minifier which does support ES6 syntax, we recommend using Babili.
boolean, defaults to false.
Enable "loose" transformations for any plugins in this preset that allow them.
"amd" | "umd" | "systemjs" | "commonjs" | false, defaults to "commonjs".
Enable transformation of ES6 module syntax to another module type.
Setting this to false will not transform modules.
boolean, defaults to false.
Outputs the targets/plugins used and the version specified in plugin data version to console.log.
Array<string>, defaults to [].
NOTE:
whitelistis deprecated and will be removed in the next major in favor of this.
An array of plugins to always include.
Valid options include any of the babel plugins or built-ins, such as transform-es2015-arrow-functions, map, set, or object.assign.
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 transform-es2015-classes transform needs to be included, as it is not possible to transpile a spread with super otherwise.
Array<string>, 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 "blacklisting" a transform like 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.
boolean, defaults to false.
A way to apply babel-preset-env for polyfills (via "babel-polyfill").
NOTE: This does not currently polyfill experimental/stage-x built-ins like the regular "babel-polyfill" does. This will only work with npm >= 3 (which should be used with Babel 6 anyway)
npm install babel-polyfill --save
This option enables a new plugin that replaces the statement import "babel-polyfill" or require("babel-polyfill") with individual requires for babel-polyfill based on environment.
NOTE: Only use
require("babel-polyfill");once in your whole app. One option is to create a single entry file that only contains the require statement.
In
import "babel-polyfill";Out (different based on environment)
import "core-js/modules/es7.string.pad-start";
import "core-js/modules/es7.string.pad-end";
import "core-js/modules/web.timers";
import "core-js/modules/web.immediate";
import "core-js/modules/web.dom.iterable";This will also work for core-js directly (import "core-js";)
npm install core-js --save
export class A {}.babelrc
{
"presets": [
["env", {
"targets": {
"chrome": 52
}
}]
]
}Out
class A {}
exports.A = A;.babelrc
{
"presets": [
["env", {
"targets": {
"chrome": 52
},
"modules": false,
"loose": true
}]
]
}Out
export class A {}.babelrc
{
"presets": [
["env", {
"targets": {
"chrome": 52,
"browsers": ["last 2 versions", "safari 7"]
}
}]
]
}Out
export var A = function A() {
_classCallCheck(this, A);
};.babelrc
{
"presets": [
["env", {
"targets": {
"node": "current"
}
}]
]
}Out
class A {}
exports.A = A;.babelrc
{
"presets": [
[ "env", {
"targets": {
"safari": 10
},
"modules": false,
"useBuiltIns": true,
"debug": true
}]
]
}stdin
Using targets:
{
"safari": 10
}
Modules transform: false
Using plugins:
transform-exponentiation-operator {}
transform-async-to-generator {}
Using polyfills:
es7.object.values {}
es7.object.entries {}
es7.object.get-own-property-descriptors {}
web.timers {}
web.immediate {}
web.dom.iterable {}always include arrow functions, explicitly exclude generators
{
"presets": [
["env", {
"targets": {
"browsers": ["last 2 versions", "safari >= 7"]
},
"include": ["transform-es2015-arrow-functions", "es6.map"],
"exclude": ["transform-regenerator", "es6.set"]
}]
]
}If you get a SyntaxError: Unexpected token ... error when using the object-rest-spread transform then make sure the plugin has been updated to, at least, v6.19.0.