code: function loadScript(options, cb) {
    if (!options) {
      throw new Error('Can\'t load nothing...');
    }
  
    // Allow for the simplest case, just passing a `src` string.
    if (type(options) === 'string') {
      options = { src : options };
    }
  
    var https = document.location.protocol === 'https:' || document.location.protocol === 'chrome-extension:';
  
    // If you use protocol relative URLs, third-party scripts like Google
    // Analytics break when testing with `file:` so this fixes that.
    if (options.src && options.src.indexOf('//') === 0) {
      options.src = (https ? 'https:' : 'http:') + options.src;
    }
  
    // Allow them to pass in different URLs depending on the protocol.
    if (https && options.https) {
      options.src = options.https;
    } else if (!https && options.http) {
      options.src = options.http;
    }
  
    // Make the `<script>` element and insert it before the first script on the
    // page, which is guaranteed to exist since this Javascript is running.
    var script = document.createElement('script');
    script.type = 'text/javascript';
    script.async = true;
    script.src = options.src;
  
    // If we have a cb, attach event handlers. Does not work on < IE9 because
    // older browser versions don't register element.onerror
    if (type(cb) === 'function') {
      onload(script, cb);
    }
  
    tick(function() {
      // Append after event listeners are attached for IE.
      var firstScript = document.getElementsByTagName('script')[0];
      firstScript.parentNode.insertBefore(script, firstScript);
    });
  
    // Return the script element in case they want to do anything special, like
    // give it an ID or attributes.
    return script;
  }
docs: Loads a script asynchronously.
  
  @param {Object} options
  @param {Function} cb