iframe-api.js

/**
 * @author       Rob W <gwnRob@gmail.com>
 * @website      https://stackoverflow.com/a/7513356/938089
 * @version      20190409
 * @description  Executes function on a framed YouTube video (see website link)
 *               For a full list of possible functions, see:
 *               https://developers.google.com/youtube/js_api_reference
 * @param String frame_id The id of (the div containing) the frame
 * @param String func     Desired function to call, eg. "playVideo"
 *        (Function)      Function to call when the player is ready.
 * @param Array  args     (optional) List of arguments to pass to function func*/
function callPlayer(frame_id, func, args) {
    if (window.jQuery && frame_id instanceof jQuery) frame_id = frame_id.get(0).id;
    var iframe = document.getElementById(frame_id);
    if (iframe && iframe.tagName.toUpperCase() != 'IFRAME') {
        iframe = iframe.getElementsByTagName('iframe')[0];
    }

    // When the player is not ready yet, add the event to a queue
    // Each frame_id is associated with an own queue.
    // Each queue has three possible states:
    //  undefined = uninitialised / array = queue / 0 = ready
    if (!callPlayer.queue) callPlayer.queue = {};
    var queue = callPlayer.queue[frame_id],
        domReady = document.readyState == 'complete';

    if (domReady && !iframe) {
        // DOM is ready and iframe does not exist. Log a message
        window.console && console.log('callPlayer: Frame not found; id=' + frame_id);
        if (queue) clearInterval(queue.poller);
    } else if (func === 'listening') {
        // Sending the "listener" message to the frame, to request status updates
        if (iframe && iframe.contentWindow) {
            func = '{"event":"listening","id":' + JSON.stringify(''+frame_id) + '}';
            iframe.contentWindow.postMessage(func, '*');
        }
    } else if ((!queue || !queue.ready) && (
        !domReady ||
        iframe && !iframe.contentWindow ||
        typeof func === 'function')) {
        if (!queue) queue = callPlayer.queue[frame_id] = [];
        queue.push([func, args]);
        if (!('poller' in queue)) {
            // keep polling until the document and frame is ready
            queue.poller = setInterval(function() {
                callPlayer(frame_id, 'listening');
            }, 250);
            // Add a global "message" event listener, to catch status updates:
            messageEvent(1, function runOnceReady(e) {
                if (!iframe) {
                    iframe = document.getElementById(frame_id);
                    if (!iframe) return;
                    if (iframe.tagName.toUpperCase() != 'IFRAME') {
                        iframe = iframe.getElementsByTagName('iframe')[0];
                        if (!iframe) return;
                    }
                }
                if (e.source === iframe.contentWindow) {
                    // Assume that the player is ready if we receive a
                    // message from the iframe
                    clearInterval(queue.poller);
                    queue.ready = true;
                    messageEvent(0, runOnceReady);
                    // .. and release the queue:
                    while (tmp = queue.shift()) {
                        callPlayer(frame_id, tmp[0], tmp[1]);
                    }
                }
            }, false);
        }
    } else if (iframe && iframe.contentWindow) {
        // When a function is supplied, just call it (like "onYouTubePlayerReady")
        if (func.call) return func();
        // Frame exists, send message
        iframe.contentWindow.postMessage(JSON.stringify({
            "event": "command",
            "func": func,
            "args": args || [],
            "id": frame_id
        }), "*");
    }
    /* IE8 does not support addEventListener... */
    function messageEvent(add, listener) {
        var w3 = add ? window.addEventListener : window.removeEventListener;
        w3 ?
            w3('message', listener, !1)
            :
            (add ? window.attachEvent : window.detachEvent)('onmessage', listener);
    }
}

observer.js

let options = {
    root: null,
    rootMargin: '0px',
    threshold: 0.2
};

function videoObserver(){
    let callback = (entries, observer) => {
        entries.forEach(entry => {
            if (entry.intersectionRatio >= 0.2) {
                entry.target.play();
            }
            else {
                entry.target.pause();
            }
        });
    }

    let observer = new IntersectionObserver(callback, options);
    const videos = document.querySelectorAll("video");

    videos.forEach(vide => {
        observer.observe(vide);
    });
}

function iframeObserver() {
    let callback = (entries, observer) => {
        entries.forEach(entry => {
            let url = new URL(entry.target.src)

            if(url.hostname === 'www.youtube.com' && url.searchParams.has('enablejsapi') && url.searchParams.has('enablejsapi') === "1") {
                id = url.pathname.split('/').pop()

                entry.target.setAttribute('id', id)

                if (entry.intersectionRatio >= 0.2) {
                    callPlayer(id, 'playVideo')
                }
                else {
                    callPlayer(id, 'pauseVideo')
                }
            }
        });
    }

    let observer = new IntersectionObserver(callback, options);
    const iframes = document.querySelectorAll("iframe");

    iframes.forEach(iframe => {
        observer.observe(iframe);
    });
}

window.addEventListener('load', () => {
    videoObserver();
    iframeObserver();
})