The JS required by Phoenix is included in the Elixir dependency, and relatively referenced by the build script. As for other JS dependencies, if you need them,

The JS required by Phoenix is included in the Elixir dependency, and relatively referenced by the build script. As for other JS dependencies, if you need them, you can add npm, webpack, or whatever you need. But they're making the statement here that not all web apps will need that. LiveView, for instance could get you pretty far. But this is distinguishing between JS in your app and JS in your build system, which until recently was necessary even for just bundling your CSS and JS.