Removes watched videos from playlist either by %watched or removes all videos of that playlist // tampermonkey

Youtube_Playlist_Cleanser.js

// ==UserScript==
// @name         Youtube Playlist Cleanser 1.0
// @namespace    Youtube Playlist Cleanser 1.0
// @version      1.0
// @description  Removes watched videos from playlist either by %watched or all
// @author       Acendro
// @include      http*://*.youtube.com/*
// @include      http*://youtube.com/*
// @include      http*://*.youtu.be/*
// @include      http*://youtu.be/*
// @run-at       document-end
// ==/UserScript==

// Config
var show_on_all = false;           //Set to true do display buttons on all playlists; overwrites next option
var playlists = ["MyPlaylist1", "AnotherOne"];   //If option above == false then display buttons on those playlists only
var threshold = 90;                //Delete if watched more or equal to % of video
var sleeptimer = 600;              //Sleep interval for cleanse function (seems to need to be quite high for consistent results)
var sleeptimer_short = 50;         //Sleep interval for Delete ALL function
// Config

const sleep = (timeout) => new Promise(res => setTimeout(res, timeout))

function CreateButton(){

    var buttonDiv = document.createElement("div");
    buttonDiv.id = "CleanseButton";

    var cleanseButton = document.createElement("button");
    cleanseButton.textContent = 'Cleanse';
    //cleanseButton.appendChild(document.createTextNode("Cleanse"));

    cleanseButton.style.width = "75px";
    cleanseButton.style.height = "100%";
    cleanseButton.style.backgroundColor = "#181717";
    cleanseButton.style.color = "white";
    cleanseButton.style.textAlign = "center";
    cleanseButton.style.fontSize = "14px";
    cleanseButton.style.border = "0";
    cleanseButton.style.cursor = "pointer";
    cleanseButton.style.borderRadius = "2px";
    cleanseButton.style.fontFamily = "Roboto, Arial, sans-serif";
    cleanseButton.style.borderRadius = "2px";
    cleanseButton.style.marginLeft = "10px";

    buttonDiv.appendChild(cleanseButton);

    buttonDiv.addEventListener("click", function() {
        playlist_cleanser();
    });

    var targetElement = document.querySelectorAll(".dropdown-trigger")[1];
    insertAfter(targetElement, buttonDiv);


    var buttonDivTwo = document.createElement("div");
    buttonDivTwo.id = "CleanseButtonTwo";

    var cleanseButtonTwo = document.createElement("button");
    //cleanseButtonTwo.appendChild(document.createTextNode("All"));
    cleanseButtonTwo.textContent = 'ALL';

    cleanseButtonTwo.style.width = "75px";
    cleanseButtonTwo.style.height = "100%";
    cleanseButtonTwo.style.backgroundColor = "#ff0000";
    cleanseButtonTwo.style.color = "white";
    cleanseButtonTwo.style.textAlign = "center";
    cleanseButtonTwo.style.fontSize = "14px";
    cleanseButtonTwo.style.border = "0";
    cleanseButtonTwo.style.cursor = "pointer";
    cleanseButtonTwo.style.borderRadius = "2px";
    cleanseButtonTwo.style.fontFamily = "Roboto, Arial, sans-serif";
    cleanseButtonTwo.style.borderRadius = "2px";
    cleanseButtonTwo.style.marginLeft = "10px";

    buttonDivTwo.appendChild(cleanseButtonTwo);

    buttonDivTwo.addEventListener("click", function() {
        console.log("clicked");
        delete_ALL();
    });

    insertAfter(buttonDiv, buttonDivTwo);
}

function insertAfter(referenceNode, newNode) {
  referenceNode.parentNode.insertBefore(newNode, referenceNode.nextSibling);
}

async function delete_ALL() {
    console.log("delete_ALL");
    while(true){
        var logger = '';
        var playlist_title = document.querySelector('#display-dialog').querySelector('#text-displayed').innerHTML;
        var elementList = document.querySelectorAll('#contents');
        var playlist = elementList[1];
        var real_playlist = playlist.querySelector('#contents');
        //console.log(real_playlist);
        var video_one = document.querySelector('#index-container');
        //console.log(video_one);
        if(!video_one) break;
        var descendents = real_playlist.getElementsByTagName('*');
        var deleter = true;
        for(var i=0; i<descendents.length; i++){
            var element = descendents[i];
            if(deleter == true){
                if (element.id == 'video-title'){
                    var namer = element.innerHTML;
                    var link = element.href.split('&list')[0]
                    console.log("Deleting: " + namer + " -> " + link);
                }
                if(element.id == 'button'){
                    await new Promise((resolve) => {
                        setTimeout(() => {
                            element.click();
                            resolve();
                        }, sleeptimer_short);
                    });
                    //sleep(sleeptimer_short);

                    var menu = document.querySelectorAll('#contentWrapper')[2];
                    var items = menu.getElementsByTagName('*');
                    for(var y=0; y<items.length; y++){
                        if(items[y].classList.contains("ytd-menu-popup-renderer")) var menu_deleteoption = items[y];
                        if(items[y].innerHTML == playlist_title){
                            await new Promise((resolve) => {
                                setTimeout(() => {
                                    menu_deleteoption.click();
                                    deleter = false;
                                    resolve();
                                }, sleeptimer_short);
                            });
                            //sleep(sleeptimer_short);
                        }
                        if(deleter == false){
                            //console.log("break");
                            break;
                        }
                    }
                }
            }
            if(deleter == false){
                //console.log("break");
                break;
            }
        }
    }
}

async function playlist_cleanser() {
    console.log("playlist_cleanser");
    while(true){
        console.log("--------------------");
        var all_progress = document.querySelectorAll('#progress');
        var continue_on = false;
        var value_check;
        for (var z = 0; z < all_progress.length; z++) {
            value_check = all_progress[z].style.cssText.substring(0, all_progress[z].style.cssText.length - 2).split('width: ')[1];
            //console.log(value_check);
            if(value_check && value_check >= threshold){
                continue_on = true;
                break;
            }
        }
        if(continue_on == false){
            console.log("@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
            console.log("       DONE CLEANSING");
            console.log("@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
            console.log("--------------------");
            break;
        }
        console.log("Found videos in playlist that match threshold criteria");
        console.log("--------------------");
        var logger = '';
        var playlist_title = document.querySelector('#display-dialog').querySelector('#text-displayed').innerHTML;
        var elementList = document.querySelectorAll('#contents');
        var playlist = elementList[1];
        var real_playlist = playlist.querySelector('#contents');
        var descendents = real_playlist.getElementsByTagName('*');
        var deleter = false;
        for(var i=0; i<descendents.length; i++){
            var element = descendents[i];
            if(element.id == 'progress'){
                logger += "At least partly watched, checking if threshhold met";
                //console.log("At least partly watched, checking if threshhold met");
                var value = element.style.cssText.substring(0, element.style.cssText.length - 2).split('width: ')[1];
                //console.log("Watched for " + value + "%");
                logger += " | Watched for " + value + "%";
                if(value >= threshold){
                    deleter = true;
                    logger += " | Threshhold met -> delete";
                    //console.log(logger);
                    logger = '';
                    //console.log("Threshhold met -> delete");
                }
                else{
                    deleter = false;
                    logger += " | Leave in watchlist";
                    //console.log(logger);
                    logger = '';
                }
            }
            if(deleter == true){
                if (element.id == 'video-title'){
                    var namer = element.innerHTML;
                    var link = element.href.split('&list')[0]
                    console.log("Deleting: " + namer + " -> " + link);
                }
                if(element.id == 'button'){
                    await new Promise((resolve) => {
                        setTimeout(() => {
                            element.click();
                            resolve();
                        }, sleeptimer);
                    });
                    sleep(sleeptimer);

                    var menu = document.querySelectorAll('#contentWrapper')[2];
                    var items = menu.getElementsByTagName('*');
                    for(var y=0; y<items.length; y++){
                        if(items[y].classList.contains("ytd-menu-popup-renderer")) var menu_deleteoption = items[y];
                        if(items[y].innerHTML == playlist_title){
                            await new Promise((resolve) => {
                                setTimeout(() => {
                                    menu_deleteoption.click();
                                    deleter = false;
                                    resolve();
                                }, sleeptimer);
                            });
                            sleep(sleeptimer*2);
                        }
                        if(deleter == false){
                            //console.log("break");
                            break;
                        }
                    }
                }
            }
        }
    }
}

document.addEventListener("DOMContentLoaded", function(event) {
    if(document.getElementById("polymer-app") || document.getElementById("masthead") || window.Polymer){
        setInterval(function(){
            if(window.location.href.indexOf("playlist?list=") < 0) return false;

            var playlist_titler = document.querySelector('#display-dialog').querySelector('#text-displayed').innerHTML;
            if(show_on_all == true){
               if(document.getElementById("CleanseButton") === null) CreateButton();
            }
            else{
                if(playlists.includes(playlist_titler)){
                    if(document.getElementById("CleanseButton") === null) CreateButton();
                }
                else return false;
           }
        }, 100);
    }
});

Cleaned it up and updated for latest YouTube version here: https://gist.github.com/js6pak/33bdefdefac09c387f55d08c5b9526fa