code: function(obj, d) {
  	var k;
  	
  	d = typeof d === 'undefined' ? 0 : d;
  	d += 1;
  	for (k in obj) {
  		if (obj.hasOwnProperty(k) && _.isObject(obj[k])) {
  			return depth(obj[k], d);
  		}
  	}
  	return (d);	
  }
docs: calculate the hierarchical depth of an object