jQuery plug-in for summing attributes

I love functions like foreach() and map() as a way for quickly arrogating through jQuery objects. I had a requirement to create a similar function today. I’m sure it has been done before but I couldn’t a direct equivalent within jQuery itself.

The function is called sum() and takes one parameter called “callback” and is directly related to it’s namesake in the map() function. The purpose of the function is to sum an attribute of each of the given elements. The “callback” parameter is a function that allows you to select the element’s attribute to be summed.

The summing component of the plug-in was taken from a code snippet on DZone.

The complete code along with an example is listed below:

/// <reference path="jquery-1.3.2-vsdoc.js" />

(function ($) {
 if (!Array.prototype.sum)
  Array.prototype.sum = function () {
   for (var i = 0, sum = 0; i < this.length; sum += this[i++]);
   return sum;
  };

 $.fn.sum = function (callback) {
  return this.map(callback).get().sum();
 };
})(jQuery);

var heightOfFirstElement = $(".element").height();
var combinedHeightOfAllElements = $(".element").sum(function () { return $(this).height(); });