The regular expression will extract the video ID from any YouTube URL and it works with shortened URLs youtu.be and embed URLs that in the format youtube.com/embed.

function extractVideoID(url) {
  var regExp = /^.*((youtu.be\/)|(v\/)|(\/u\/\w\/)|(embed\/)|(watch\?))\??v?=?([^#\&\?]*).*/;
  var match = url.match(regExp);
  if (match && match[7].length == 11) {
    return match[7];
  } else {
    alert('Could not extract video ID.');
  }
}

Another alternative that will extract the video ID as well as the playlist ID from YouTube URLS:

var id = url.match('v=([a-zA-Z0-9_-]+)&?')[1];
var list = url.match('list=([a-zA-Z0-9-_]+)&?');
list = list ? list[1] : '';