Zoom to layer when layer is turned on

Question

I am new to javascript. I have a web page with a web map that is hosted on ArcGIS Online, and a legend that lets the user turn on and off the layers. I want to zoom to the extent of the last layer that was turned on. I am not sure how to get information about the layers in the web map, such as extent. Thanks in advance. Here is my code: CDTA System Map

Routes

---- dashed lines are limited service

BRT Routes

Trunk Routes

Neighborhood Routes

Express Routes

Commuter Routes

JakeSkinner · Answer

I believe you could do something like below:checkBox = new CheckBox({
    name : "chk" + layer.title,
    checked : layer.layer.visible,
    value : layer.title,
    onChange : function() {                                                                                        
      if (layer.layer.featureCollection) {
        dojo.forEach(layer.layer.featureCollection.layers, function(layer) {                          
          layer.layerObject.setVisibility(!layer.layerObject.visible);
        });
      } else {

layer.layer.setVisibility(!layer.layer.visible);

} 
      if(this.checked){
        map.setExtent(layer.layer.fullExtent);
      }
    } 
  });

However, your service will need to be in the same spatial reference (102100 - WGS 1984 Web Mercator (Aux Sphere)) as the map.