element-registry-directive.js

angular.module('utils.ElementRegistryDemo',[])
.directive('elem', function(ElementRegistry) {
  return {
    restrict: 'A',
    scope: false,
    link:function(scope, element, attrs){
      // store this element with reference to the parent scope
      new ElementRegistry(scope).add(attrs.elem, element);
    }
  };
})
.factory('ElementRegistry', function () {
  var id,             // scope id to store on the class
      waitingFor={};  // dictionary of callbacks we are waiting for

  function ElementRegistry(scope){
    id = scope.$id;
    // initialize class stores if they are undefined
    ElementRegistry.store = ElementRegistry.store || {};
    ElementRegistry.store[id] = ElementRegistry.store[id] || {};
  }

  // get a key from the store
  function findByKey(key){
    return ElementRegistry.store[id][key] ? ElementRegistry.store[id][key] : false;
  }

  // hold on to a call back until it is needed
  function storeCallback(key, callback){
    waitingFor[key] = callback;
  }

  // run the stored callback
  function fireCallback(key){
    if(waitingFor[key]){
      waitingFor[key](findByKey(key));
    }
  }

  ElementRegistry.prototype = {

    // return the found value otherwise run a callback once found
    find: function(key, callback){
      var found = findByKey(key);

      
      if(!found){
        storeCallback(key, callback);
        return;
      }

      if(callback){
        callback(found);
      }

      return found;
    },

    // add an element to the scope store
    add: function(key, value){
      ElementRegistry.store[id][key] = value;
      fireCallback(key);
    },

    // return the storage object
    store: function(){
      return ElementRegistry.store[id];
    }
  };

  return ElementRegistry;

}]);