zulip/docs/subsystems/front-end-build-process.md

Static asset pipeline

This page documents additional information that may be useful when developing new features for Zulip that require front-end changes, especially those that involve adding new files. For a more general overview, see the new feature tutorial.

Our dependencies documentation has useful relevant background as well.

Primary build process

Most of the existing JS in Zulip is written in IIFE-wrapped modules, one per file in the static/js directory. We will over time migrate this to Typescript modules. In development mode files are loaded using webpack eval with sourcemaps. In production mode (and when creating a release tarball using tools/build-release-tarball), JavaScript files are concatenated and minified. We use the django pipeline extension to manage our static assets, webpack, and typescript. The main internal tool that does all of this work is tools/update-prod-static, which is called by both tools/build-release-tarball and tools/upgrade-zulip-from-git.

Adding static files

To add a static file to the app (JavaScript, CSS, images, etc), first add it to the appropriate place under static/.

• Third-party files that we haven't patched should be installed via yarn, so that it's easy to upgrade them and third-party code doesn't bloat the Zulip repository. You can then access them in webpack.assets.json via their paths under node_modules. You'll want to add these to the package.json in the root of the repository, and then provision (to have yarn download them) before continuing. Your commit should also update PROVISION_VERSION in version.py. When adding modules to package.json, please pin specific versions of them (don't using carets ^, tildes ~, etc). We prefer fixed versions so that when the upstream providers release new versions with incompatible APIs, it can't break Zulip. We update those versions periodically to ensure we're running a recent version of third-party libraries.
• Third-party files that we have patched should all go in static/third/. Tag the commit with "[third]" when adding or modifying a third-party package. Our goal is to the extent possible to eliminate patched third-party code from the project.
• Our own JavaScript lives under static/js.
• Typescript files live under static/ts.
• CSS lives under static/styles.
• Portico JavaScript ("portico" means for logged-out pages) lives under static/js/portico.
• Custom SVG graphics living under static/assets/icons are compiled into custom icon webfonts that live under static/generated/icons/fonts by tools/setup/generate-custom-icon-webfont according to the static/icons/fonts/template.hbs template.

After you add a new JavaScript file, it needs to be imported by another file or specified in the entries dictionary defined in tools/webpack.assets.json to be included in the concatenated file; this will magically ensure it is available both in development and production. CSS should be added to the STYLESHEETS section of PIPELINE in zproject/settings.py. A few notes on doing this:

• For new files you should generally import it from another file rather than adding it to tools/webpack.assets.json
• If you plan to only use the JS/CSS within the app proper, and not on the login page or other standalone pages, put it in the app bundle.
• If you plan to use it in both, put it in the common bundle.
• If it's just used on a single standalone page (e.g. /stats), give it its own bundle. To load a bundle in the relevant Jinja2 template for that page, use render_bundle and stylesheet for JS and CSS, respectively.
• If you modify tools/webpack.assets.json you will need to restart the server.

If you want to test minified files in development, look for the PIPELINE_ENABLED = line in zproject/settings.py and set it to True -- or just set DEBUG = False.

Note that static/html/5xx.html will only render properly if minification is enabled, since they, by nature, hardcode the path static/min/portico.css.

How it works in production

You can learn a lot from reading about django-pipeline, but a few useful notes are:

• Zulip installs static assets in production in /home/zulip/prod-static. When a new version is deployed, before the server is restarted, files are copied into that directory.
• We use the VFL (Versioned File Layout) strategy, where each file in the codebase (e.g. favicon.ico) gets a new name (e.g. favicon.c55d45ae8c58.ico) that contains a hash in it. Each deployment, has a manifest file (e.g. /home/zulip/deployments/current/staticfiles.json) that maps codebase filenames to serving filenames for that deployment. The benefit of this VFL approach is that all the static files for past deployments can coexist, which in turn eliminates most classes of race condition bugs where browser windows opened just before a deployment can't find their static assets. It also is necessary for any incremental rollout strategy where different clients get different versions of the site.
• Some paths for files (e.g. emoji) are stored in the rendered_content of past messages, and thus cannot be removed without breaking the rendering of old messages (or doing a mass-rerender of old messages).

Webpack/CommonJS/ES6/Typescript modules

New JS written for Zulip can be written as Typescript or if a more incremental migration is required, CommonJS modules (bundled using webpack, though this will be taken care of automatically whenever run-dev.py is running). (CommonJS is the same module format that Node uses, so see the Node documentation for more information on the syntax.)

All JavaScript we provide will eventually be migrated to Typescript, which will make refactoring the frontend code easier and allow static analyzers to reason about our code more easily.

Declare entry points in webpack.assets.json. Any modules you add will need to be imported from this file (or one of its dependencies) in order to be included in the script bundle.

Hot Reloading

Webpack support hot reloading. To enable it you will need to add

// This reloads the module in development rather than refreshing the page
if (module.hot) {
    module.hot.accept();
}

To the entry point of any JavaScript file you want to hot reload rather than refeshing the page on a change.