Eat Your Food - Netflix Interruptor

userscript.js

// ==UserScript==
// @name         Remember to eat your food while watching Netflix
// @namespace    https://www.tarikguney.com
// @version      0.1
// @description  Kids watching cartoons on Netflix often forget to eat and chew their food, which drives parents crazy. You need to sit down with them and pause the video and remind them to eat their food. This script will automate that.
// @author       Tarik Guney
// @match        https://www.netflix.com/watch/*
// @icon         https://upload.wikimedia.org/wikipedia/commons/thumb/7/75/Netflix_icon.svg/1200px-Netflix_icon.svg.png
// @grant        none
// ==/UserScript==

(function() {
    'use strict';
    var interruptionInterval = 40000; // 40 seconds
    var pauseTime = 8000; // 8 seconds

    var interruptionIntervalId;
    if(document.readyState === 'ready' || document.readyState === 'complete') {
        console.info("page is ready");
        interruptionIntervalId = startInterruptingNetflix();
    } else {
        document.onreadystatechange = function () {
            if (document.readyState == "complete") {
                console.info("page is ready");
                interruptionIntervalId = startInterruptingNetflix();
            }
        }
    }
    // If moving onto the next video in line, rebind the timer.
    let lastUrl = location.href;
    new MutationObserver(() => {
        const url = location.href;
        if (url !== lastUrl) {
            lastUrl = url;
            onUrlChange();
        }
    }).observe(document, {subtree: true, childList: true});

    async function onUrlChange() {
        console.info("Playing the next video");
        clearInterval(interruptionIntervalId);
        await new Promise(resolve => setTimeout(resolve, pauseTime));
        interruptionIntervalId = startInterruptingNetflix();
    }

    async function startInterruptingNetflix(){
        var mediaPlayer = document.getElementsByTagName("video")[0];
        var maximumRetryBucket = 1000;
        while(mediaPlayer == null && maximumRetryBucket >= 0){
            await new Promise(resolve => setTimeout(resolve, 1000));
            mediaPlayer = document.getElementsByTagName("video")[0];
            maximumRetryBucket--;
        }

        if(mediaPlayer == null){
            console.error("the netflix media player could not be found!");
        }

        console.info("the netflix media player is found");
        return setInterval(function(){
            if(mediaPlayer.readyState >= 2 && mediaPlayer.paused == false){
                mediaPlayer.pause();
                console.info("the media player is paused");
                setTimeout(function(){
                    var actualPlayPromise = mediaPlayer.play();
                    actualPlayPromise.then(_ => {
                        console.info("the media player resumes");
                    });

                },pauseTime);
            }

        },interruptionInterval);
    }
})();

I've made some small changes:

1. Defined initializationDelay, interruptionInterval, and pauseTime to better explain which number is what.
2. Added known issues that I found out.
3. Added comment for an area of improvement.
4. Increased the pause to 8 seconds, which is a more sufficient amount of time for kids to take a bite of their food.
5. Increased the initializationDelay variable to 10 seconds after having tested the script on a slower computer.

When Netflix video jumps to the next in line, the script loses its effect. Looks like the jump happens w/o page refresh.

I've find something like this to trigger script again when URL location changed.

May It helps: https://stackoverflow.com/a/52809105/3369359

Thanks @gokaybiz!

Corrected:

1. No more problem when automatically playing the next video in line.
2. I removed the initializationDelay, now checking for the mediaPlayer in a loop.