youtube-reverse-playlist.user.js

// ==UserScript==
// @name           Example from http://stackoverflow.com/q/6834930
// @version        1.3
// @namespace      http://stackoverflow.com/q/6834930
// @description    Allow reverse playlist in Youtube
// @include        https://www.youtube.com/*
// ==/UserScript==

function load(url, onLoad, onError) {
    e = document.createElement("script");
    e.setAttribute("src", url);

    if (onLoad != null) { e.addEventListener("load", onLoad); }
    if (onError != null) { e.addEventListener("error", onError); }

    document.head.appendChild(e);

    return e;
}

function execute(functionOrCode) {
    if (typeof functionOrCode === "function") {
        code = "(" + functionOrCode + ")();";
    } else {
        code = functionOrCode;
    }

    e = document.createElement("script");
    e.textContent = code;

    document.head.appendChild(e);

    return e;
}

function loadAndExecute(url, functionOrCode) {
    load(url, function() { execute(functionOrCode); });
}

loadAndExecute("//ajax.googleapis.com/ajax/libs/jquery/1.6.2/jquery.min.js", function() {
    console.log("New script loaded...");

//    console.log($(".playlist-videos-list"));

$(document).ready(function() {

$(".playlist-videos-list>li").each(function() {
    $(element).attr('data-index', 0);
});

console.log($(".playlist-videos-list>li"));

});

});