Scouting file by Alex Sexton

scout.js

// From: http://alexsexton.com/blog/2013/03/deploying-javascript-applications/
// Simplified example of a scout file
(function () {
  // Feature test some stuff
  var features = {
    svg: Modernizr.svg,
    touch: Modernizr.touch
  };

  // The async script injection fanfare
  var script = document.createElement('script');
  var fScript = document.getElementsByTagName('script')[0];

  var baseUrl = '//cool-cdn.com/bucket/' + __BUILDNUM__ + '/';


  // Build up a file url based on the features of this user
  var featureString = '';
  for (var i in features) {
    if (features.hasOwnProperty(i) && features[i]) {
      featuresString += '-' + i;
    }
  }
  var package = 'build' + featureString + '.js'

  // Set the URL on the script
  script.src = baseUrl + package;

  // Inject the script
  fScript.parentNode.insertBefore(script, fScript);

  // Start loading the data that you know you can grab right away
  // JSONP is small and easy to kick off for this.
  var dataScript = document.createElement('script');

  // Create a JSONP Url based on some info we have.
  // We'll assume localstorage for this example
  // though a cookie or url param might be safer.

  window.appInitData = function (initialData) {
    // Get it to the core application when it eventually
    // loads or if it's already there.
    // A global is used here for ease of example
    window.comeGetMe = initialData;
  };

  // If we're on a static site, the url might tell us
  // the data we need, and the user cookie might customize
  // it. Simplified.
  dataScript.src = '//api.mysite.com' +
                   document.location.pathname +
                   '?userid=' +
                   localStorage.getItem('userid') +
                   '&callback=appInitData;';

  // Inject it
  fScript.parentNode.insertBefore(dataScript, fScript);
})();