gistfile1.js

(function (w, d) {
	// See: https://gist.github.com/1250370
	// See: http://d.hatena.ne.jp/amachang/20070611/1181554170

	var slice = Array.prototype.slice;

	var BoxHeight = function (tagName, object) {
		this.top = 0;
		this.height = 0;
		this.target = [];

		this.call(tagName, object);
	};

	BoxHeight.prototype = {
		call: function (tagName, object) {
			var self = this;
			var parent = this.$(object) || d;
			var elements = parent.getElementsByTagName(tagName);

			this.applyEach(slice.call(elements), function (e, i) {
				var style = self.getStyle(e);

				if (e.offsetTop !== self.top) {
					if(self.target.length > 1) {
						self.applyEach(self.target, self.setHeight, self.height);
					}

					self.target = [];
					self.height = 0;
					self.top = e.offsetTop;
				}

				self.target.push(e);

				self.height = Math.max(
					parseInt(self.getStyle(e).height, 10),
					parseInt(self.height, 10)
				);
			});
		},

		setHeight: function (e, i, height) {
			// binded context
			e.style.height = height.toString() + 'px';
		},

		getStyle: function (element) {
			return element.currentStyle || d.defaultView.getComputedStyle(element, '');
		},

		$: function (object) {
			if (object.nodeType && object.nodeType === 1) {
				return object;
			}

			return document.getElementById(object);
		},

		applyEach: function (collection, iterator) {
			var args = slice.call(arguments, 2);
			var result = [];

			for (var i = 0, l = collection.length; i < l; i++) {
				result.push(iterator.apply(null, [collection[i], i].concat(args)));
			}

			return result;
		}
	}

	w.BoxHeight = BoxHeight;

})(window, document);