code: function(key, value) {
          if (arguments.length === 1) {
              return Crafty.assets[key];
          }
  
          if (!Crafty.assets[key]) {
              Crafty.assets[key] = value;
              this.trigger("NewAsset", {key : key, value : value});
          }
      }
docs: @
  #Crafty.asset
  @category Assets
  
  @trigger NewAsset - After setting new asset - Object - key and value of new added asset.
  @sign public void Crafty.asset(String key, Object asset)
  @param key - asset url.
  @param asset - Audio` or `Image` object.
  Add new asset to assets object.
  
  @sign public void Crafty.asset(String key)
  @param key - asset url.
  Get asset from assets object.
  
  @example
  ~~~
  Crafty.asset(key, value);
  var asset = Crafty.asset(key); //object with key and value fields
  ~~~
  
  @see Crafty.assets