AngularJS, RequireJS, AlmondJS, and Google Maps

I had to solve the problem of integrating AngularJS and RequireJS with Google Maps. This is not usually a huge challenge, there is even an async module for RequireJS, and an Angular-UI map plugin to make integration pretty seamless. The wrinkle that made this integration trickier is AlmondJS—and Almond doesn’t support asynchronous module loading.

When you include the Google Maps script, you can specify a callback in the querystring that will fire when the Google Maps API is loaded. You could then bootstrap your Angular app in that callback, e.g.:

    function mapReady() {
      angular.bootstrap(document.getElementById("gmap"), ['app.ui-map']);

    <!-- funky formatting to fit the whole url on the screen -->

This will work, but it will block your app until you hear back from Google Maps. I didn’t want to do that; there was only one spot where a user might use the map. Therefore, I wanted to lazily load it.

When you are configuring the $routeProvider, you can specify an object for the route parameter’s resolve property. Each property on the resolve object is a function that can return a promise. The controller will not get instantiated until the promise is resolved. And when the promise is resolved, the value returned from the promise resolution gets passed into the controller as a parameter.

So the plan of action was to resolve a promise when Google Maps was ready.

    // ...
      path: '/path/to/where/ever',
      controller: 'SomeCtrl',
      route: {
        resolve: {
          gmap: function() {
            var dfd = $q.defer();
            // load google maps
            // fire callback
            // resolve promise
            return dfd.promise;

Here’s more-or-less how I implemented the gmap function.

    gmap: function() {
      var dfd = $q.defer();
      var doc = $window.document;
      var scriptId = 'gmapScript';
      var scriptTag = doc.getElementById(scriptId);

      if (scriptTag) {
        // if `scriptTag` exists, then gmaps must be available, so...
        return true;

      // load google maps
      scriptTag = doc.createElement('script'); = scriptId;

      // fire callback, specified in the callback attribute of the script tag's src 
      // attribute.
      // The callback has to be in global (window) scope, so that Google Maps can find
      // it. I used a closure to store a reference to the deferred object we will 
      // resolve when the callback is fired.
      $window.mapReady = (function(dfd) {
        return function() {
          // resolve the promise:
          // cleanup the global space now that we are done:
          delete $window.mapReady;
      return dfd.promise;

With this approach, we don’t risk blocking the entire app; just this one route might block. Of course, this example just shows how to handle the “happy path”; it doesn’t handle if the Maps API fails to load for some reason. I also wound up extending it to return the current positions coordinates, instead of just true when the maps API is ready. That is left as an exercise for the reader …

Buzz de Cafe 15 November 2013