src/docs/optimizing_web_uis.md

Optimizing Chrome Web UIs

How do I do it?

In order to build with a fast configuration, try setting these options in your GN args:

optimize_webui = true
is_debug = false

How is the code optimized?

Bundling

JS Modules are used heavily throughout the code. Fetching all imports and their transitive dependencies can be slow, especially when there are too many requests during initial page load.

To reduce this latency, Chrome uses Rollup to bundle the code into a couple JS bundle files (usually one or two). This greatly decreases latency of initial load, by eliminating the overhead that is associated with each individual request.

JavaScript Minification

In order to minimize disk size, we run terser on all combined JavaScript. This reduces installer and the size of resources required to load to show a UI.

Code like this:

function fizzBuzz() {
  for (var i = 1; i <= 100; i++) {
    var fizz = i % 3 == 0 ? 'fizz' : '';
    var buzz = i % 5 == 0 ? 'buzz' : '';
    console.log(fizz + buzz || i);
  }
}
fizzBuzz();

would be minified to:

function fizzBuzz(){for(var z=1;100>=z;z++){var f=z%3==0?"fizz":"",o=z%5==0?"buzz":"";console.log(f+o||z)}}fizzBuzz();

If you'd like to more easily debug minified code, click the "{}" prettify button in Chrome's developer tools, which will beautify the code and allow setting breakpoints on the un-minified version.

Gzip compression of web resources

As of r761031 all HTML, JS, CSS and SVG resources are compressed by default with gzip Previously this was only happening if the compress="gzip" attribute was specified as follows in the corresponding .grd file:

<include name="IDR_MY_PAGE" file="my/page.html" type="BINDATA" compress="gzip" />

This is no longer necessary, and should be omitted. Only specify the compress attribute if the value is false or brotli.

Compressed resources are uncompressed at a fairly low layer within ResourceBundle, and WebUI authors typically do not need to do anything special to serve those files to the UI.