sw-precache

by GoogleChromeLabs

GoogleChromeLabs / sw-precache

[Deprecated] A node module to generate service worker code that will precache specific resources so ...

5.3K Stars 433 Forks Last release: almost 3 years ago (5.2.1) Apache License 2.0 462 Commits 15 Releases

Available items

No Items, yet!

The developer of this repository has not created any items for sale yet. Need a bug fixed? Help with integration? A different license? Create a request here:

⚠️ sw-precache ⚠️

sw-toolbox
and
sw-precache
are deprecated in favor of Workbox. Please read this migration guide for information on upgrading.

About

Service Worker Precache is a module for generating a service worker that precaches resources. It integrates with your build process. Once configured, it detects all your static resources (HTML, JavaScript, CSS, images, etc.) and generates a hash of each file's contents. Information about each file's URL and versioned hash are stored in the generated service worker file, along with logic to serve those files cache-first, and automatically keep those files up to date when changes are detected in subsequent builds.

Serving your local static resources cache-first means that you can get all the crucial scaffolding for your web app—your App Shell—on the screen without having to wait for any network responses.

The module can be used in JavaScript-based build scripts, like those written with

gulp
, and it also provides a command-line interface. You can use the module directly, or if you'd prefer, use one of the wrappers around

sw-precache
for specific build environments, like
webpack
.

It can be used alongside the

sw-toolbox
library, which works well when following the App Shell + dynamic content model.

The full documentation is in this README, and the getting started guide provides a quicker jumping off point.

To learn more about the internals of the generated service worker, you can read this deep-dive by Huang Xuan.

Table of Contents

Install

Local build integration:

sh
$ npm install --save-dev sw-precache

Global command-line interface:

sh
$ npm install --global sw-precache

Usage

Overview

  1. Make sure your site is served using HTTPS! Service worker functionality is only available on pages that are accessed via HTTPS. (

    http://localhost
    will also work, to facilitate testing.) The rationale for this restriction is outlined in the "Prefer Secure Origins For Powerful New Features" document.
  2. Incorporate

    sw-precache
    into your
    node
    -based build script.
    It should work well with either

    gulp
    or
    Grunt
    , or other build scripts that run on
    node
    . In fact, we've provided examples of both in the
    demo/
    directory. Each build script in
    demo
    has a function called
    writeServiceWorkerFile()
    that shows how to use the API. Both scripts generate fully-functional JavaScript code that takes care of precaching and fetching all the resources your site needs to function offline. There is also a command-line interface available, for those using alternate build setups.
  3. Register the service worker JavaScript. The JavaScript that's generated needs to be registered as the controlling service worker for your pages. This technically only needs to be done from within a top-level "entry" page for your site, since the registration includes a

    scope
    which will apply to all pages underneath your top-level page.
    service-worker-registration.js
    is a sample script that illustrates the best practices for registering the generated service worker and handling the various lifecycle events.

Example

The project's sample

gulpfile.js
illustrates the full use of sw-precache in context. (Note that the sample gulpfile.js is the one in the

demo
folder, not the one in the root of the project.) You can run the sample by cloning this repo, using
npm install
to pull in the dependencies, changing to the
demo/
directory, running
`npm bin`/gulp serve-dist
, and then visiting http://localhost:3000.

There's also a sample

Gruntfile.js
that shows service worker generation in Grunt. Though, it doesn't run a server on localhost.

Here's a simpler gulp example for a basic use case. It assumes your site's resources are located under

app
and that you'd like to cache all your JavaScript, HTML, CSS, and image files.
gulp.task('generate-service-worker', function(callback) {
  var swPrecache = require('sw-precache');
  var rootDir = 'app';

swPrecache.write(${rootDir}/service-worker.js, { staticFileGlobs: [rootDir + '/*/.{js,html,css,png,jpg,gif,svg,eot,ttf,woff}'], stripPrefix: rootDir }, callback); });

This task will create

app/service-worker.js
, which your client pages need to register before it can take control of your site's pages.
service-worker-registration.js
is a ready-to- use script to handle registration.

Considerations

  • Service worker caching should be considered a progressive enhancement. If you follow the model of conditionally registering a service worker only if it's supported (determined by

    if('serviceWorker' in navigator)
    ), you'll get offline support on browsers with service workers and on browsers that don't support service workers, the offline-specific code will never be called. There's no overhead/breakage for older browsers if you add
    sw-precache
    to your build.
  • All resources that are precached will be fetched by a service worker running in a separate thread as soon as the service worker is installed. You should be judicious in what you list in the

    dynamicUrlToDependencies
    and
    staticFileGlobs
    options, since listing files that are non-essential (large images that are not shown on every page, for instance) will result in browsers downloading more data than is strictly necessary.
  • Precaching doesn't make sense for all types of resources (see the previous point). Other caching strategies, like those outlined in the Offline Cookbook, can be used in conjunction with

    sw-precache
    to provide the best experience for your users. If you do implement additional caching logic, put the code in a separate JavaScript file and include it using the
    importScripts()
    method.
  • sw-precache
    uses a cache-first strategy, which results in a copy of any cached content being returned without consulting the network. A useful pattern to adopt with this strategy is to display a toast/alert to your users when there's new content available, and give them an opportunity to reload the page to pick up that new content (which the service worker will have added to the cache, and will be available at the next page load). The sample
    service-worker-registration.js
    file illustrates the service worker lifecycle event you can listen for to trigger this message.

Command-line interface

For those who would prefer not to use

sw-precache
as part of a
gulp
or
Grunt
build, there's a command-line interface which supports the options listed in the API, provided via flags or an external JavaScript configuration file.

Hypenated flags are converted to camelCase options.
Options starting with

--no
prefix negate the boolean value. For example,
--no-clients-claim
sets the value of
clientsClaim
to
false
.

Warning: When using

sw-precache
"by hand", outside of an automated build process, it's your responsibility to re-run the command each time there's a change to any local resources! If
sw-precache
is not run again, the previously cached local resources will be reused indefinitely.

Sensible defaults are assumed for options that are not provided. For example, if you are inside the top-level directory that contains your site's contents, and you'd like to generate a

service-worker.js
file that will automatically precache all of the local files, you can simply run
$ sw-precache

Alternatively, if you'd like to only precache

.html
files that live within
dist/
, which is a subdirectory of the current directory, you could run
$ sw-precache --root=dist --static-file-globs='dist/**/*.html'

Note: Be sure to use quotes around parameter values that have special meanings to your shell (such as the

*
characters in the sample command line above, for example).

Finally, there's support for passing complex configurations using

--config 
. Any of the options from the file can be overridden via a command-line flag. We strongly recommend passing it an external JavaScript file defining config via
module.exports
. For example, assume there's a
path/to/sw-precache-config.js
file that contains:
module.exports = {
  staticFileGlobs: [
    'app/css/**.css',
    'app/**.html',
    'app/images/**.*',
    'app/js/**.js'
  ],
  stripPrefix: 'app/',
  runtimeCaching: [{
    urlPattern: /this\\.is\\.a\\.regex/,
    handler: 'networkFirst'
  }]
};

That file could be passed to the command-line interface, while also setting the

verbose
option, via
$ sw-precache --config=path/to/sw-precache-config.js --verbose

This provides the most flexibility, such as providing a regular expression for the

runtimeCaching.urlPattern
option.

We also support passing in a JSON file for

--config
, though this provides less flexibility:
{
  "staticFileGlobs": [
    "app/css/**.css",
    "app/**.html",
    "app/images/**.*",
    "app/js/**.js"
  ],
  "stripPrefix": "app/",
  "runtimeCaching": [{
    "urlPattern": "/express/style/path/(.*)",
    "handler": "networkFirst"
  }]
}

Runtime Caching

It's often desireable, even necessary to use precaching and runtime caching together. You may have seen our

sw-toolbox
tool, which handles runtime caching, and wondered how to use them together. Fortunately,

sw-precache
handles this for you.

The

sw-precache
module has the ability to include the
sw-toolbox
code and configuration alongside its own configuration. Using the
runtimeCaching
configuration option in
sw-precache
(see below) is a shortcut that accomplishes what you could do manually by importing
sw-toolbox
in your service worker and writing your own routing rules.

API

Methods

The

sw-precache
module exposes two methods:
generate
and
write
.

generate(options, callback)

generate
takes in options, generates a service worker from them and passes the result to a callback function, which must have the following interface:

callback(error, serviceWorkerString)

In the 1.x releases of

sw-precache
, this was the default and only method exposed by the module.

Since 2.2.0,

generate()
also returns a
Promise
.

write(filePath, options, callback)

write
takes in options, generates a service worker from them, and writes the service worker to a specified file. This method always invokes
callback(error)
. If no error was found, the
error
parameter will be
null

Since 2.2.0,

write()
also returns a
Promise
.

Options Parameter

Both the

generate()
and
write()
methods take the same options.

cacheId [String]

A string used to distinguish the caches created by different web applications that are served off of the same origin and path. While serving completely different sites from the same URL is not likely to be an issue in a production environment, it avoids cache-conflicts when testing various projects all served off of

http://localhost
. You may want to set it to, e.g., the
name
property from your
package.json
.

Default:

''

clientsClaim [Boolean]

Controls whether or not the generated service worker will call

clients.claim()
inside the

activate
handler.

Calling

clients.claim()
allows a newly registered service worker to take control of a page immediately, instead of having to wait until the next page navigation.

Default:

true

directoryIndex [String]

Sets a default filename to return for URL's formatted like directory paths (in other words, those ending in

'/'
).
sw-precache
will take that translation into account and serve the contents a relative
directoryIndex
file when there's no other match for a URL ending in
'/'
. To turn off this behavior, set
directoryIndex
to
false
or
null
. To override this behavior for one or more URLs, use the
dynamicUrlToDependencies
option to explicitly set up mappings between a directory URL and a corresponding file.

Default:

'index.html'

dontCacheBustUrlsMatching [Regex]

It's very important that the requests

sw-precache
makes to populate your cache result in the most up-to-date version of a resource at a given URL. Requests that are fulfilled with out-of-date responses (like those found in your browser's HTTP cache) can end up being read from the service worker's cache indefinitely. Jake Archibald's blog post provides more context about this problem.

In the interest of avoiding that scenario,

sw-precache
will, by default, append a cache-busting parameter to the end of each URL it requests when populating or updating its cache. Developers who are explicitly doing "the right thing" when it comes to setting HTTP caching headers on their responses might want to opt out of this cache-busting. For example, if all of your static resources already include versioning information in their URLs (via a tool like
gulp-rev
), and are served with long-lived HTTP caching headers, then the extra cache-busting URL parameter is not needed, and can be safely excluded.

dontCacheBustUrlsMatching
gives you a way of opting-in to skipping the cache busting behavior for a subset of your URLs (or all of them, if a catch-all value like
/./
is used). If set, then the pathname of each URL that's prefetched will be matched against this value. If there's a match, then the URL will be prefetched as-is, without an additional cache-busting URL parameter appended.

Note: Prior to

sw-precache
v5.0.0,
dontCacheBustUrlsMatching
matched against the entire request URL. As of v5.0.0, it only matches against the URL's pathname.

Default: not set

dynamicUrlToDependencies [Object⟨String,Buffer,Array⟨String⟩⟩]

Maps a dynamic URL string to an array of all the files that URL's contents depend on. E.g., if the contents of

/pages/home
are generated server-side via the templates
layout.jade
and
home.jade
, then specify
'/pages/home':
['layout.jade', 'home.jade']
. The MD5 hash is used to determine whether
/pages/home
has changed will depend on the hashes of both
layout.jade
and
home.jade
.

An alternative value for the mapping is supported as well. You can specify a string or a Buffer instance rather than an array of file names. If you use this option, then the hash of the string/Buffer will be used to determine whether the URL used as a key has changed. For example,

'/pages/dynamic': dynamicStringValue
could be used if the contents of
/pages/dynamic
changes whenever the string stored in
dynamicStringValue
changes.

Default:

{}

handleFetch [boolean]

Determines whether the

fetch
event handler is included in the generated service worker code. It is useful to set this to
false
in development builds, to ensure that features like live reload still work. Otherwise, the content would always be served from the service worker cache.

Default:

true

ignoreUrlParametersMatching [Array⟨Regex⟩]

sw-precache
finds matching cache entries by doing a comparison with the full request URL. It's common for sites to support URL query parameters that don't affect the site's content and should be effectively ignored for the purposes of cache matching. One example is the
utm_
-prefixed
parameters used for tracking campaign performance. By default,
sw-precache
will ignore
key=value
when
key
matches any of the regular expressions provided in this option. To ignore all parameters, use
[/./]
. To take all parameters into account when matching, use
[]
.

Default:

[/^utm_/]

importScripts [Array⟨String⟩]

Writes calls to

importScripts()
to the resulting service worker to import the specified scripts.

Default:

[]

logger [function]

Specifies a callback function for logging which resources are being precached and a precache size. Use

function() {}
if you'd prefer that nothing is logged. Within a
gulp
script, it's recommended that you use
gulp-util
and pass in
gutil.log
.

Default:

console.log

maximumFileSizeToCacheInBytes [Number]

Sets the maximum allowed size for a file in the precache list.

Default:

2097152
(2 megabytes)

navigateFallback [String]

Sets an HTML document to use as a fallback for URLs not found in the

sw-precache
cache. This fallback URL needs to be cached via
staticFileGlobs
or
dynamicUrlToDependencies
otherwise it won't work.
// via staticFileGlobs
staticFileGlobs: ['/shell.html']
navigateFallback: '/shell.html'

// via dynamicUrlToDependencies dynamicUrlToDependencies: { '/shell': ['/shell.hbs'] }, navigateFallback: '/shell'

This comes in handy when used with a web application that performs client-side URL routing using the History API. It allows any arbitrary URL that the client generates to map to a fallback cached HTML entry. This fallback entry ideally should serve as an "application shell" that is able to load the appropriate resources client-side, based on the request URL.

Note: This is not intended to be used to route failed navigations to a generic "offline fallback" page. The

navigateFallback
page is used whether the browser is online or offline. If you want to implement an "offline fallback", then using an approach similar to this example is more appropriate.

Default:

''

navigateFallbackWhitelist [Array⟨RegExp⟩]

Works to limit the effect of

navigateFallback
, so that the fallback only applies to requests for URLs with paths that match at least one
RegExp
.

This option is useful if you want to fallback to the cached App Shell for certain specific subsections of your site, but not have that behavior apply to all of your site's URLs.

For example, if you would like to have

navigateFallback
only apply to navigation requests to URLs whose path begins with
/guide/
(e.g.
https://example.com/guide/1234
), the following configuration could be used:
navigateFallback: '/shell',
navigateFallbackWhitelist: [/^\/guide\//]

If set to

[]
(the default), the whitelist will be effectively bypassed, and
navigateFallback
will apply to all navigation requests, regardless of URL.

Default:

[]

replacePrefix [String]

Replaces a specified string at the beginning of path URL's at runtime. Use this option when you are serving static files from a different directory at runtime than you are at build time. For example, if your local files are under

dist/app/
but your static asset root is at
/public/
, you'd strip 'dist/app/' and replace it with '/public/'.

Default:

''

runtimeCaching [Array⟨Object⟩]

Configures runtime caching for dynamic content. If you use this option, the

sw-toolbox
library configured with the caching strategies you specify will automatically be included in your generated service worker file.

Each

Object
in the
Array
needs a
urlPattern
, which is either a
RegExp
or a string, following the conventions of the
sw-toolbox
library's routing configuration. Also required is a
handler
, which should be either a string corresponding to one of the built-in handlers under the
toolbox.
namespace, or a function corresponding to your custom request handler. Optionally,
method
can be added to specify one of the supported HTTP methods (default:
'get'
). There is also support for
options
, which corresponds to the same options supported by a
sw-toolbox
handler
.

For example, the following defines runtime caching behavior for two different URL patterns. It uses a different handler for each, and specifies a dedicated cache with maximum size for requests that match

/articles/
:
runtimeCaching: [{
  urlPattern: /^https:\/\/example\.com\/api/,
  handler: 'networkFirst'
}, {
  urlPattern: /\/articles\//,
  handler: 'fastest',
  options: {
    cache: {
      maxEntries: 10,
      name: 'articles-cache'
    }
  }
}]

The

sw-precache
+
sw-toolbox
explainer
has more information about how and why you'd use both libraries together.

Default:

[]

skipWaiting [Boolean]

Controls whether or not the generated service worker will call

skipWaiting()
inside the

install
handler.

By default, when there's an update to a previously installed service worker, then the new service worker delays activation and stays in a

waiting
state until all pages controlled by the old service worker are unloaded. Calling
skipWaiting()
allows a newly registered service worker to bypass the
waiting
state.

When

skipWaiting
is
true
, the new service worker's
activate
handler will be called immediately, and any out of date cache entries from the previous service worker will be deleted. Please keep this in mind if you rely on older cached resources to be available throughout the page's lifetime, because, for example, you defer the loading of some resources until they're needed at runtime.

Default:

true

staticFileGlobs [Array⟨String⟩]

An array of one or more string patterns that will be passed in to

glob
. All files matching these globs will be automatically precached by the generated service worker. You'll almost always want to specify something for this.

Default:

[]

stripPrefix [String]

Removes a specified string from the beginning of path URL's at runtime. Use this option when there's a discrepancy between a relative path at build time and the same path at run time. For example, if all your local files are under

dist/app/
and your web root is also at
dist/app/
, you'd strip that prefix from the start of each local file's path in order to get the correct relative URL.

Default:

''

stripPrefixMulti [Object]

Maps multiple strings to be stripped and replaced from the beginning of URL paths at runtime. Use this option when you have multiple discrepancies between relative paths at build time and the same path at run time. If

stripPrefix
and
replacePrefix
are not equal to
''
, they are automatically added to this option.
js
stripPrefixMulti: {
  'www-root/public-precached/': 'public/',
  'www-root/public/': 'public/'
}

Default:

{}

templateFilePath [String]

The path to the (lo-dash) template used to generate

service-worker.js
. If you need to add additional functionality to the generated service worker code, it's recommended that you use the
importScripts
option to include extra JavaScript rather than using a different template. But if you do need to change the basic generated service worker code, please make a copy of the original template, modify it locally, and use this option to point to your template file.

Default:

service-worker.tmpl
(in the directory that this module lives in)

verbose [boolean]

Determines whether there's log output for each individual static/dynamic resource that's precached. Even if this is set to false, there will be a final log entry indicating the total size of all precached resources.

Default:

false

Wrappers and Starter Kits

While it's possible to use the

sw-precache
module's API directly within any JavaScript environment, several wrappers have been developed by members of the community tailored to specific build environments. They include: -
sw-precache-webpack-plugin
-
sw-precache-brunch
-
grunt-sw-precache
-
exhibit-builder-sw-precache

There are also several starter kits or scaffolding projects that incorporate

sw-precache
into their build process, giving you a full service worker out of the box. The include:

CLIs

Starter Kits

Recipes for writing a custom wrapper

While there are not always ready-to-use wrappers for specific environments, this list contains some recipes to integrate

sw-precache
in your workflow:

Acknowledgements

Thanks to Sindre Sorhus and Addy Osmani for their advice and code reviews. Jake Archibald was kind enough to review the service worker logic.

License

Copyright © 2017 Google, Inc.

Licensed 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.

We use cookies. If you continue to browse the site, you agree to the use of cookies. For more information on our use of cookies please see our Privacy Policy.