Name: preload-webpack-plugin
Owner: GoogleChromeLabs
Description: A Webpack plugin for wiring up `` (and prefetch) - supports async chunks
Created: 2017-01-26 18:06:06.0
Updated: 2018-01-16 15:32:27.0
Pushed: 2018-01-13 06:05:04.0
Size: 423
Language: JavaScript
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A Webpack plugin for automatically wiring up asynchronous (and other types) of JavaScript
chunks using <link rel='preload'>. This helps with lazy-loading.
Note: This is an extension plugin for html-webpack-plugin - a plugin that simplifies the creation of HTML files to serve your webpack bundles.
This plugin is a stop-gap until we add support for asynchronous chunk wiring to script-ext-html-webpack-plugin.
Preload is a web standard aimed at improving performance and granular loading of resources. It is a declarative fetch that can tell a browser to start fetching a source because a developer knows the resource will be needed soon. Preload: What is it good for? is a recommended read if you haven't used the feature before.
In simple web apps, it's straight-forward to specify static paths to scripts you would like to preload - especially if their names or locations are unlikely to change. In more complex apps, JavaScript can be split into “chunks” (that represent routes or components) at with dynamic names. These names can include hashes, numbers and other properties that can change with each build.
For example, chunk.31132ae6680e598f8879.js.
To make it easier to wire up async chunks for lazy-loading, this plugin offers a drop-in way to wire them up
using <link rel='preload'>.
This module requires Webpack 2.2.0 and above. It also requires that you're using html-webpack-plugin in your Webpack project.
First, install the package as a dependency in your package.json:
m install --save-dev preload-webpack-plugin
Alternatively, using yarn:
add -D preload-webpack-plugin
Next, in your Webpack config, require() the preload plugin as follows:
t PreloadWebpackPlugin = require('preload-webpack-plugin');
and finally, configure the plugin in your Webpack plugins array after HtmlWebpackPlugin:
ins: [
w HtmlWebpackPlugin(),
w PreloadWebpackPlugin()
When preloading files, the plugin will use different as attribute depends on the type of each
file. For each file ends with .css, the plugin will preload it with as=style, for each file ends
with .woff2, the plugin will preload it with as=font, while for all other files, as=script
will be used.
If you do not prefer to determine as attribute depends on suffix of filename, you can also
explicitly name it using as:
ins: [
w HtmlWebpackPlugin(),
w PreloadWebpackPlugin({
rel: 'preload',
as: 'script'
In case you need more fine-grained control of the as atribute, you could also provide a function here.
When using it, entry name will be provided as the parameter, and function itself should return a
string for as attribute:
ins: [
w HtmlWebpackPlugin(),
w PreloadWebpackPlugin({
rel: 'preload',
as(entry) {
if (/\.css$/.test(entry)) return 'style';
if (/\.woff$/.test(entry)) return 'font';
if (/\.png$/.test(entry)) return 'image';
return 'script';
}
Notice that if as=font is used in preload, crossorigin will be added, otherwise the font resource
might be double fetched. Explains can be found in this article.
By default, the plugin will assume async script chunks will be preloaded. This is the equivalent of:
ins: [
w HtmlWebpackPlugin(),
w PreloadWebpackPlugin({
rel: 'preload',
include: 'asyncChunks'
For a project generating two async scripts with dynamically generated names, such as
chunk.31132ae6680e598f8879.js and chunk.d15e7fdfc91b34bb78c4.js, the following preloads
will be injected into the document <head>:
k rel="preload" as="script" href="chunk.31132ae6680e598f8879.js">
k rel="preload" as="script" href="chunk.d15e7fdfc91b34bb78c4.js">
You can also configure the plugin to preload all chunks (vendor, async, normal chunks) using include: 'all', or only preload initial chunks with include: 'initial':
ins: [
w HtmlWebpackPlugin(),
w PreloadWebpackPlugin({
rel: 'preload',
include: 'all' // or 'initial'
In case you work with named chunks, you can explicitly specify which ones to include by passing an array:
ins: [
w HtmlWebpackPlugin(),
w PreloadWebpackPlugin({
rel: 'preload',
include: ['home']
will inject just this:
k rel="preload" as="script" href="home.31132ae6680e598f8879.js">
There may be chunks that you don't want to have preloaded (sourcemaps, for example). Before preloading each chunk, this plugin checks that the file does not match any regex in the fileBlacklist option. The default value of this blacklist is [/\.map/], meaning no sourcemaps will be preloaded. You can easily override this:
PreloadWebpackPlugin({
leBlacklist: [/\.whatever/]
Passing your own array will override the default, so if you want to continue filtering sourcemaps along with your own custom settings, you'll need to include the regex for sourcemaps:
PreloadWebpackPlugin({
leBlacklist: [/\.map/, /\.whatever/]
Should you wish to use Resource Hints (such as prefetch) instead of preload, this plugin also supports wiring those up.
Prefetch:
ins: [
w HtmlWebpackPlugin(),
w PreloadWebpackPlugin({
rel: 'prefetch'
For the async chunks mentioned earlier, the plugin would update your HTML to the following:
k rel="prefetch" href="chunk.31132ae6680e598f8879.js">
k rel="prefetch" href="chunk.d15e7fdfc91b34bb78c4.js">
A demo application implementing the PRPL pattern with React that uses this plugin can be found in the demo
directory.
If you've found an error in this sample, please file an issue: https://github.com/googlechrome/preload-webpack-plugin/issues
Patches are encouraged, and may be submitted by forking this project and submitting a pull request through GitHub.
index.js contains the primary source for the plugin, test contains tests and demo contains demo code.
Test the plugin:
m install
m run test
Lint the plugin:
m run lint
m run lint-fix # fix linting issues
The project is written in ES2015, but does not use a build-step. This may change depending on any Node version support requests posted to the issue tracker.
preload resources a user is unlikely to need. This can waste their bandwidth.preload for the current session if you think a user is likely to visit the next page. There is no
100% guarantee preloaded items will end up in the HTTP Cache and read locally beyond this session.prefetch and preconnect. Prefetched resources are maintained
in the HTTP Cache for at least 5 minutes (in Chrome) regardless of the resource's cachability.Copyright 2017 Google, Inc.
Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to you under the Apache License, Version 2.0 (the “License”); you may not use this file except in compliance with the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.