no-youtube.user.js

// ==UserScript==
// @name     no-youtube
// @description		Replace youtube links to invisio.us 
// @version  1.0.2
// @grant    none
// @require        https://code.jquery.com/jquery-2.2.2.js
// @run-at        document-end
// ==/UserScript==

var j = jQuery.noConflict(true);

j(document).ready(function ($) {
  var longURL = "youtube.com/";
  var shortURL = "youtu.be/";

  $('a').click(function (event) {
    var currentLocation = window.location.href;
    var txt = $(event.target).text();

    if (!(currentLocation.includes(longURL)) && !(currentLocation.includes("invidio.us/") && txt.includes("Watch on YouTube"))) {
      var addressValue = $(this).attr("href");
      var target = $(this).attr("target");
      console.log("target: " + target);
      if (event.ctrlKey || event.metaKey) {
        target = "_blank";
      }
      if (addressValue.includes(longURL)) {
        event.preventDefault();
        generateUrl(addressValue, target, longURL);
      } else if (addressValue.includes(shortURL)) {
        event.preventDefault();
        generateUrl(addressValue, target, shortURL);
      }
    }
  });
});

function generateUrl(addressValue, target, ytURL) {
  var splitstring = addressValue.split(ytURL);
  var url = "https://invidio.us/" + splitstring[splitstring.length - 1];
  console.log("url: " + url);
  window.open(url, target);
}