Load up scripts using Promises in Lightning

ScriptLoadHelper.js

getResouce: function(component, scriptName, resourceName) {
  return new Promise($A.getCallback(function(resolve, reject) {

    if (component.get("v.scriptsLoaded") == true) {
      resolve(window[scriptName]);
    } 
    else {

      // Create script element and set attributes
      var script = document.createElement('script');
      script.type = 'text/javascript';
      script.async = true;
      script.src = resourceName;

      var el = document.getElementsByClassName('scriptdiv')[0];
      el.parentNode.insertBefore(script, el);

      // Resolve the promise once the script is loaded
      script.addEventListener('load', () => {
        component.set("v.scriptsLoaded", true);
        resolve(window[scriptName]);
      });

      // Catch any errors while loading the script
      script.addEventListener('error', () => {
        reject('script failed to load');
      });
    }

  }))
},