Javascript to download YouTube videos - Moral Volcano

// ==UserScript==
// @name        Download any YouTube video from anywhere
// @namespace   com.vsubhash.js.youtube.download
// @description Adds a download button to YouTube videos including those embedded elsewhere
// @version     1
// @grant       none
// ==/UserScript==

/*
 * Moral Volcano's YouTub DL JavaScript
 * https://moralvolcano.wordpress.com/2015/05/09/how-to-download-any-youtube-video-using-just-javascript-no-need-for-any-special-add-on-or-extension-in-opera-12x-or-older/
 * Licensed under GPL v3 as provided at
 * https://www.gnu.org/licenses/gpl.html
 *
 */

document.addEventListener("DOMContentLoaded", addYouTubeDetectingButton(), false);

function addYouTubeDetectingButton() {
  console.log("User JS called");
  var i, n, oDlButtonEl, oDlDiv, oVidLink;

  if ((location.href.indexOf("youtube.com/embed") != -1) ||
      (location.href.indexOf("youtube.com/watch") != -1)) {
    console.log("Inside YouTube Iframe");

    oDlDiv = document.createElement("div");
    oDlDiv.setAttribute("id", "mvJsDiv");
    oDlDiv.setAttribute("style", "color: black; background-color: orange!important; width: 100%!important; height: 1.2cm!important; font-size: 0.34cm!important; line-height: 0.4cm!important; font-family: sans-serif!important;  ");

    oDlButtonEl = document.createElement("input");
    oDlDiv.setAttribute("id", "mvJsButton");
    oDlButtonEl.setAttribute("type", "button");
    oDlButtonEl.setAttribute("value", "Grab Video");

    oDlButtonEl.addEventListener("click", handle_DownloadButtonClick, false);

    oDlButtonEl.setAttribute("style", "color: white!important; border: 1px solid orange; box-shadow: 2px 2px 5px black; background-color: red!important; height: 0.9cm!important; width: 5cm!important; font-size: 0.4cm!important; line-height: 0.5cm!important; ; font-family: sans-serif!important;");
    oDlDiv.appendChild(oDlButtonEl);

    oVidLink = document.createElement("a");
    oVidLink.setAttribute("id", "mvJsLink");
    oVidLink.setAttribute("style", "color: darkblue!important; text-decoration: underline!important; font-size: 0.3cm!important; margin: 0.2cm 1cm 0.2cm 1cm!important;");
    oVidLink.innerHTML="Video URL";
    oVidLink.setAttribute("href","javascript:window.alert('First play the video a bit and pause. Then, we will get the video link.');");
    oDlDiv.appendChild(oVidLink);


    document.getElementById("player").setAttribute("style", document.getElementById("player").getAttribute("style") + "height: 90%!important; ");

    document.getElementById("player").parentNode.insertBefore(oDlDiv, document.getElementById("player"));

    document.getElementsByTagName("body")[0].style="background-color: white!important; line-height: 0.5cm;";
    document.getElementById("player").parentNode.style="background-color: white!important; ";


  }
}

function handle_DownloadButtonClick() {
  if (document.getElementsByTagName("video").length > 0) {
   if (document.getElementsByTagName("video")[0].src.length > 10) {
     document.getElementById("mvJsLink").setAttribute("href",document.getElementsByTagName("video")[0].src + "&title=" + document.title+".flv");

     document.getElementById("mvJsLink").innerHTML = document.getElementsByTagName("video")[0].src.substring(0,35) + "...";

     location.href=document.getElementsByTagName("video")[0].src + "&title=" + document.title+".flv";

   } else {
     window.alert("First play the video a bit and pause. Then, we will get the video link.");
   }
  } else {
    window.alert("No video has loaded yet.");
  }
}