analytics.js loader for rails

analytics_js_loader.js.erb

// sources: https://segment.io/libraries/analytics.js#getting-started
//          https://github.com/phillbaker/analytics-js-rails/blob/master/app/views/analytics-js/_loader.html.erb

// Create a queue, but don't obliterate an existing one!
window.analytics || (window.analytics = []);

// A list of all the methods in analytics.js that we want to stub.
window.analytics.methods = ['identify', 'track', 'trackLink', 'trackForm',
'trackClick', 'trackSubmit', 'page', 'pageview', 'ab', 'alias', 'ready',
'group', 'on', 'once', 'off'];

// Define a factory to create queue stubs. These are placeholders for the
// "real" methods in analytics.js so that you never have to wait for the library
// to load asynchronously to actually track things. The `method` is always the
// first argument, so we know which method to replay the call into.
window.analytics.factory = function (method) {
  return function () {
    var args = Array.prototype.slice.call(arguments);
    args.unshift(method);
    // see https://github.com/segmentio/analytics.js/issues/253#issuecomment-24280169
    if(!window.analytics.push){
      window.analytics.push = Array.prototype.push.bind(window.analytics);
    }
    window.analytics.push(args);
    return window.analytics;
  };
};

// For each of our methods, generate a queueing method.
for (var i = 0; i < window.analytics.methods.length; i++) {
  var method = window.analytics.methods[i];
  window.analytics[method] = window.analytics.factory(method);
}

// Define a method that will asynchronously load analytics.js from our CDN.
window.analytics.load = function (callback) {

  // Create an async script element for analytics.js based on your API key.
  var script = document.createElement('script');
  script.type = 'text/javascript';
  script.async = true;
  script.src = '<%= asset_path("analytics.min.js") %>';

  script.addEventListener('load', function (e) {
    if(typeof callback == 'function') {
      callback(e);
    }
  }, false);

  // Find the first script element on the page and insert our script next to it.
  var firstScript = document.getElementsByTagName('script')[0];
  firstScript.parentNode.insertBefore(script, firstScript);
};

// Add a version so we can keep track of what's out there in the wild.
window.analytics.SNIPPET_VERSION = '2.0.6';

window.analytics.load(function() {
  window.analytics.initialize({
    'Google Analytics' : {classic: true,
                          siteSpeedSampleRate: 100,
                          trackingId: '<%= config.analytics_account %>'},
    'Mixpanel': {token: '<%= config.mixpanel_account %>',
                 people: true},
    'trak.io': '<%= config.trakio_account %>'
  });
});