to load external Javascript on browser console

var el = document.createElement("script"),
loaded = false;
el.onload = el.onreadystatechange = function () {
  if ((el.readyState && el.readyState !== "complete" && el.readyState !== "loaded") || loaded) {
    return false;
  }
  el.onload = el.onreadystatechange = null;
  loaded = true;
  // done!
};
el.async = true;
el.src = '//cdnjs.cloudflare.com/ajax/libs/underscore.js/1.7.0/underscore-min.js';
var hhead = document.getElementsByTagName('head')[0];
hhead.insertBefore(el, hhead.firstChild);