YT_ScrollNLoad_Playlist.user.js

// ==UserScript==
// @name            Youtube: Space to go to bottom of playlist
// @description     Load playlist until everything is displayed and scrolls down if needed.
// @author          Wosser1's Productions
// @namespace       https://gist.github.com/Wosser1sProductions/
// @icon            https://youtube.com/favicon.ico
// @version         0.3.1
// @include         http*://*.youtube.com/playlist?list=*
// @include         http*://*.youtube.com/*
// @include         http*://youtube.com/*
// @include         http*://*.youtu.be/*
// @include         http*://youtu.be/*
// @exclude         http*://*.youtube.com/watch?v=*
// ==/UserScript==

var loadID;

function getMoreBtn() {
    return document.querySelector('button.load-more-button');
}

function scrollAndLoad() {
    var moreButton = getMoreBtn();

    if (moreButton !== null) {
        moreButton.click();
    } else {
        //window.removeEventListener('keydown', setLoadInterval);
        window.clearInterval(loadID);
    }
    window.scrollTo(0,document.body.scrollHeight);
}

function setLoadInterval(e) {
    var validTarget = e.target === document.body;

    if (validTarget && e.keyCode === 32) {
        e.preventDefault();
        window.scrollTo(0,document.body.scrollHeight);
        if (!loadID)
            if (getMoreBtn())
                loadID = window.setInterval(scrollAndLoad, 100 );
    }
}

window.addEventListener('keydown', e => setLoadInterval(e));