code: function(list, func) {
  		list = list || []; func = func || function(){return false;};
  		for (var i = 0, l = list.length; i < l; i++) {
  			if (func(list[i])){ return i; }
  		}
  		return -1;
  	}
docs: ### indexBy*(list, func)* The default underscore indexOf uses a literal value; we often want to use an comparator. This function returns the index of the first element in the list that the comparator returns truthy when evaluating, or -1 if no elements match.