youtube-music/plugins/captions-selector/front.js

const { ElementFromFile, templatePath } = require("../utils");
const { ipcRenderer } = require("electron");

function $(selector) { return document.querySelector(selector); }

const captionsSettingsButton = ElementFromFile(
    templatePath(__dirname, "captions-settings-template.html")
);

module.exports = (options) => {
    document.addEventListener('apiLoaded', (event) => setup(event, options), { once: true, passive: true });
}

/**
 * If captions are disabled by default,
 * unload "captions" module when video changes.
 */
const videoChanged = (api, options) => {
    if (options.disableCaptions) {
        setTimeout(() => api.unloadModule("captions"), 100);
    }
}

function setup(event, options) {
    const api = event.detail;

    $("video").addEventListener("srcChanged", () => videoChanged(api, options));

    $(".right-controls-buttons").append(captionsSettingsButton);

    captionsSettingsButton.onclick = async () => {
        api.loadModule("captions");

        const captionTrackList = api.getOption("captions", "tracklist");

        if (captionTrackList?.length) {
            const currentCaptionTrack = api.getOption("captions", "track");
            let currentIndex = !currentCaptionTrack ?
				null :
				captionTrackList.indexOf(captionTrackList.find(track => track.languageCode === currentCaptionTrack.languageCode));

            const captionLabels = [
                ...captionTrackList.map(track => track.displayName),
                'None'
            ];

            currentIndex = await ipcRenderer.invoke('captionsSelector', captionLabels, currentIndex)
			if (currentIndex === null) return;

			const newCaptions = captionTrackList[currentIndex];
			if (newCaptions) {
				api.setOption("captions", "track", { languageCode: newCaptions.languageCode });
			} else {
				api.setOption("captions", "track", {});
			}

			setTimeout(() => api.playVideo());
        }
    }
}