Asset Versioning & Cache Busting

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There is one last thing I want to talk about, and it's one of my favorite features in Encore. Here's the question: how can we version our assets? Or, even more simple, how can we bust browser cache? For example, right now, if I change something in RepLogApp.js, then of course Webpack will create an updated rep_log.js file. But, when an existing user comes back to our site, their browser might use the old, cached version! Lame!

Enabling Versioning

This is a classic problem. But with Encore, we can solve it beautifully and automatically! In webpack.config.js, first add .cleanupOutputBeforeBuild():

32 lines | webpack.config.js
// ... lines 1 - 3
// ... lines 5 - 25
// ... line 27
// ... lines 29 - 32

That's a nice little function that will empty the public/build directory whenever you run Encore. Then, here's the key: .enableVersioning():

32 lines | webpack.config.js
// ... lines 1 - 3
// ... lines 5 - 25
// ... lines 29 - 32

That's it! Because we just changed our config, restart Encore:

yarn watch

Now look at the build/ directory. Woh! Suddenly, all of our files have a hash in the filename! The hash is based on the file's contents: so whenever the file changes, it gets a new filename. This is awesome! Now when rep_log.js changes, it will have a new filename. And when we deploy to production, the user's browser will see the new filename and load it, instead of using the old, cached version.

Versioned Filenamed with manifest.json

Perfect! Except... we just broke everything. Find your browser and refresh. Yep! It's horrible! And this makes sense: in the base layout, our script tag simply points to build/layout.js:

107 lines | templates/base.html.twig
// ... lines 1 - 96
{% block javascripts %}
// ... lines 98 - 101
<script src="{{ asset('build/layout.js') }}"></script>
{% endblock %}
// ... lines 104 - 107

But this is not the filename anymore - it's missing the hash part!

Of course, we could type the filename manually here. But, gross! Then, every time we updated a file, we would need to update its script tag.

Here's the key to fix this. Behind the scenes, as soon as we started using Encore, it generated a manifest.json file automatically. This is a map from the source filename to the current hashed filename! That's great! If we could somehow tell Symfony's asset() function to read this and make the transformation, then, well... everything would work perfectly!

And... yea! That feature exists! Open config/packages/framework.yaml. Anywhere, but I'll do it at the bottom, add assets: then json_manifest_path set to %kernel.project_dir%/public/build/manifest.json:

38 lines | config/packages/framework.yaml
// ... lines 2 - 35
json_manifest_path: '%kernel.project_dir%/public/build/manifest.json'

This is a built-in feature that tells Symfony to look for a JSON file at this path, and to use it to lookup the real filename. In other words... just, refresh! Yea, everything is beautiful again! Check out the page source: it's using the hashed filename from the manifest file.

And if you change one of the files - like layout.js: add a console.log()... as soon as we do this, Webpack rebuilds. In the build/ directory - you might need to synchronize it, but yes! It creates a new filename. When you refresh, the system automatically uses that inside the source.

Long-Lived Expires Headers

This is free asset versioning and cache busting! If you want to get really crazy, you can also now give your site a performance boost! To do that, you'll need to configure your web server to set long-lived Expires header on any files in the /build directory.

Basically, by setting an Expires header, your web server can instruct the browser of each user to cache any downloaded assets... forever! Then, when the user continues browsing your site, it will load faster because their browser knows it's safe to use these files from cache. And of course, when we do make a change to a file in the future, the browser will download it thanks to its new filename.

The exact config is different in Nginx versus Apache, but it's a common thing to add. Google for "Nginx expires header for directory".

OK guys, I hope, hope, hope you love Webpack Encore as much as I do! It has even more features that we didn't talk about, like enableReactPreset() to build React apps or enableVueLoader() for Vue.js. And we're adding new features all the time so that it's easier to use front-end frameworks and enjoy some of the really amazing things that are coming from the JavaScript world... without needing to read 100 blog posts every day.

So get out there and write amazing JavaScript! And I hope you'll stay with us for our next tutorial about React.js & Symfony!

All right guys, seeya next time!