Using the JS API

Discourse's JavaScript API allows themes and plugins to make extensive customizations to the user experience. The simplest way to use it is to create a new theme from the admin panel, click "Edit Code", and then head to the JS tab.

For file-based themes, the API can be used by creating a file in the api-initializers directory. For theme's that's {theme}/javascripts/api-initializers/init-theme.gjs, and for plugins, it's {plugin}/assets/javascripts/discourse/api-initializers/init-plugin.js. The content should be:

import { apiInitializer } from "discourse/lib/api";

export default apiInitializer((api) => {
  // Your code here
});

All the available APIs are listed in the plugin-api.gjs source code in Discourse core, along with a short description and examples.

For a full tuturial, including examples of JS API usage, check out:

https://meta.discourse.org/t/theme-developer-tutorial-1-introduction/357796