callback.js

//if this is your callback
var callback = function(error,response){
	if(error){
		//code here would only run if error is truthy
	}else{
		//this only runs if !error ==- true
	}
	 
}
//you can also write that as
var callbackDontCare = function(error,response){
	if(!error){
		//cone if there isn't an error
	}else{
		handleError(error);//remember to define this
	}
}