script loader

scriptloader.js

function loadScript(url) {
  var head   = document.getElementsByTagName("head")[0] || document.documentElement;
  var script = document.createElement("script");

  script.setAttribute("async",   "true");
  script.setAttribute("charset", "utf-8");
  script.setAttribute("type",    "text/javascript");
  script.setAttribute("src",     url);

  //
  // Code from:
  // http://stackoverflow.com/questions/4845762/onload-handler-for-script-tag-in-internet-explorer
  // http://stevesouders.com/efws/script-onload.php
  //

  return new Promise(function(resolve) {
    // Handle Script loading
    var done = false;

    // Attach handlers for all browsers
    script.onload = script.onreadystatechange = function() {
      if (!done && (!this.readyState ||
            this.readyState === "loaded" ||
            this.readyState === "complete")) {
        done = true;

        // Get the module id that just finished and load it up!
        // var loadedSrc = script.getAttribute("src");

        // Handle memory leak in IE
        script.onload = script.onreadystatechange = null;
        if (head && script.parentNode) {
          head.removeChild(script);
        }

        resolve();
      }
    };

    head.appendChild(script);
  });
}