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README.md
This package allows transpiling JavaScript files using Babel and webpack.
Notes: Issues with the output should be reported on the babel issue tracker.
Install
webpack 1.x | babel-loader <= 6.x
webpack 2.x | babel-loader >= 7.x (recommended) (^6.2.10 will also work, but with deprecation warnings)
webpack 3.x | babel-loader >= 7.1
yarn add babel-loader babel-core babel-preset-env webpack --dev
We recommend using yarn, but you can also still use npm:
npm install --save-dev babel-loader babel-core babel-preset-env webpack
Usage
Within your webpack configuration object, you'll need to add the babel-loader to the list of modules, like so:
module: {
rules: [
{
test: /\.js$/,
exclude: /(node_modules|bower_components)/,
use: {
loader: 'babel-loader',
options: {
presets: ['env']
}
}
}
]
}
Options
See the babel
options.
You can pass options to the loader by using the options property:
module: {
rules: [
{
test: /\.js$/,
exclude: /(node_modules|bower_components)/,
use: {
loader: 'babel-loader',
options: {
presets: ['env'],
plugins: [require('babel-plugin-transform-object-rest-spread')]
}
}
}
]
}
This loader also supports the following loader-specific option:
-
cacheDirectory
: Defaultfalse
. When set, the given directory will be used to cache the results of the loader. Future webpack builds will attempt to read from the cache to avoid needing to run the potentially expensive Babel recompilation process on each run. If the value is blank (loader: 'babel-loader?cacheDirectory'
) ortrue
(loader: babel-loader?cacheDirectory=true
) the loader will use the default cache directory innode_modules/.cache/babel-loader
or fallback to the default OS temporary file directory if nonode_modules
folder could be found in any root directory. -
cacheIdentifier
: Default is a string composed by the babel-core's version, the babel-loader's version, the contents of .babelrc file if it exists and the value of the environment variableBABEL_ENV
with a fallback to theNODE_ENV
environment variable. This can be set to a custom value to force cache busting if the identifier changes. -
forceEnv
: Default will resolve BABEL_ENV then NODE_ENV. Allow you to override BABEL_ENV/NODE_ENV at the loader level. Useful for isomorphic applications with different babel configuration for client and server.
Note: The sourceMap
option is ignored, instead sourceMaps are automatically enabled when webpack is configured to use them (via the devtool
config option).
Troubleshooting
babel-loader is slow!
Make sure you are transforming as few files as possible. Because you are probably
matching /\.js$/
, you might be transforming the node_modules
folder or other unwanted
source.
To exclude node_modules
, see the exclude
option in the loaders
config as documented above.
You can also speed up babel-loader by as much as 2x by using the cacheDirectory
option.
This will cache transformations to the filesystem.
babel is injecting helpers into each file and bloating my code!
babel uses very small helpers for common functions such as _extend
. By default
this will be added to every file that requires it.
You can instead require the babel runtime as a separate module to avoid the duplication.
The following configuration disables automatic per-file runtime injection in babel, instead
requiring babel-plugin-transform-runtime
and making all helper references use it.
See the docs for more information.
NOTE: You must run npm install babel-plugin-transform-runtime --save-dev
to include this in your project and babel-runtime
itself as a dependency with npm install babel-runtime --save
.
rules: [
// the 'transform-runtime' plugin tells babel to require the runtime
// instead of inlining it.
{
test: /\.js$/,
exclude: /(node_modules|bower_components)/,
use: {
loader: 'babel-loader',
options: {
presets: ['env'],
plugins: ['transform-runtime']
}
}
}
]
NOTE: transform-runtime & custom polyfills (e.g. Promise library)
Since babel-plugin-transform-runtime includes a polyfill that includes a custom regenerator runtime and core.js, the following usual shimming method using webpack.ProvidePlugin
will not work:
// ...
new webpack.ProvidePlugin({
'Promise': 'bluebird'
}),
// ...
The following approach will not work either:
require('babel-runtime/core-js/promise').default = require('bluebird');
var promise = new Promise;
which outputs to (using runtime
):
'use strict';
var _Promise = require('babel-runtime/core-js/promise')['default'];
require('babel-runtime/core-js/promise')['default'] = require('bluebird');
var promise = new _Promise();
The previous Promise
library is referenced and used before it is overridden.
One approach is to have a "bootstrap" step in your application that would first override the default globals before your application:
// bootstrap.js
require('babel-runtime/core-js/promise').default = require('bluebird');
// ...
require('./app');
The node API for babel
has been moved to babel-core
.
If you receive this message it means that you have the npm package babel
installed and use the short notation of the loader in the webpack config (which is not valid anymore as of webpack 2.x):
{
test: /\.js$/,
loader: 'babel',
}
Webpack then tries to load the babel
package instead of the babel-loader
.
To fix this you should uninstall the npm package babel
as it is deprecated in babel v6. (instead install babel-cli
or babel-core
)
In the case one of your dependencies is installing babel
and you cannot uninstall it yourself, use the complete name of the loader in the webpack config:
{
test: /\.js$/,
loader: 'babel-loader',
}