fn.load-script

fn.load-script.js

function () {
  return function (url, callback) {
    var doc = document,
     el = doc.createElement('script');
    
    el.src = url;
    el.async = 1;
    
    if (callback) {
      el.addEventListener('load', callback);
    }
    
    doc.getElementsByTagName('head')[0].appendChild(el);
  };
}