Tuesday, November 5, 2013

Loading Google Maps API asynchronously with RequireJS

With Single Page Web Applications becoming more and more popular, I decided to understand the concepts of various Javascript frameworks a little better. There are literally hundreds of them, but I decided to start with a really nice tutorial written by Alex Young. Cornerstones in this tutorial are BackboneJS, Underscore, Bootstrap and RequireJS.

After been through the tutorial I decided to roll my own project based on the same setup. I wanted to use Google Maps for this, and searched for a way to load the API using RequireJS. Turned out that there are a few different approaches, but the most common seems to be to use the async-plugin created by Miller Medeiros.

Jason Wyatt has another interesting solution which caught my attention. Being new to all this, I really didn't feel like start involving plug-ins from remote repositories. It might be the most natural thing to do, but one step at a time is more my melody.

Jason's solution had some drawbacks mentioned in the comments of his post, such as the way Google loads itself asynchronously and how the return value will be an empty stub before everything is loaded. I guess the point is to put the actual maps implementation in the anonymous callback function, but I'd rather have more separation between the loading mechanism and the implementation. The same actually applies to the async-plugin solution, as far as I can tell.

I updated Jason's implementation to look like this:

  define(['config'], function(config) {

    function AsyncLoad(callback) {
      // create a global callback method for Google to use
      var callbackName = 'googlemaps'+(new Date()).getTime();
      window[callbackName] = callback;

      // load the api asynchronously
      require(['http://maps.googleapis.com/maps/api/js?key=' + config.apiKey + '&sensor=false&callback=' + callbackName], function(){
        // do nothing and wait for callback instead
      });
    }

    return AsyncLoad;
  });
The way to use it is to instantiate it with a callback function as an argument. And the key is to make this function operate on the calling object and not from the window object, i.e. 'this' should point to the calling object. This is where Function.prototype.bind comes in, as it creates a new function where the 'this' keyword is bound to the supplied value.

This is how to use it:

define(['asyncload'], function(AsyncLoad) {
  var App = function() {
    this.loadMaps();
  };

  App.prototype = {
    loadMaps: function() {
      var asyncLoad = new AsyncLoad(this.renderMaps.bind(this));
    },
    renderMaps: function() {
      console.log(this); // the App
      var mapOptions = {
        zoom: 8,
        center: new google.maps.LatLng(-34.397, 150.644),
        mapTypeId: google.maps.MapTypeId.ROADMAP
      }
    }
  };

  return App;
});
The callback function is bound to the App and the renderMaps-function will be called just as if it was done from the the App itself. Now, the good thing that comes out of all this is that the renderMaps-function holds all code related to Google Maps, no matter how it was loaded.