discourse/app/assets/javascripts/discourse/initializers/enable-emoji.js

import { withPluginApi } from "discourse/lib/plugin-api";
import { registerEmoji } from "pretty-text/emoji";
import PreloadStore from "preload-store";

export default {
  name: "enable-emoji",

  initialize(container) {
    const siteSettings = container.lookup("site-settings:main");
    if (!siteSettings.enable_emoji) {
      return;
    }

    withPluginApi("0.1", api => {
      api.onToolbarCreate(toolbar => {
        toolbar.addButton({
          id: "emoji",
          group: "extras",
          icon: "far-smile",
          action: () => toolbar.context.send("emoji"),
          title: "composer.emoji"
        });
      });
    });

    (PreloadStore.get("customEmoji") || []).forEach(emoji =>
      registerEmoji(emoji.name, emoji.url, emoji.group)
    );
  }
};