/* This script and many more are available free online at
The JavaScript Source!! http://javascript.internet.com
Created by: Bobby van der Sluis | http://www.bobbyvandersluis.com/ */
// Details can be found at:
// http://www.bobbyvandersluis.com/articles/unobtrusivedynamicselect.php

function dynamicSelect(id1, id2) {
 	// Feature test to see if there is enough W3C DOM support
 	if (document.getElementById && document.getElementsByTagName) {
  		// Obtain references to both select boxes
  		var sel1 = document.getElementById(id1);
  		var sel2 = document.getElementById(id2);
  		// Clone the dynamic select box
  		var clone = sel2.cloneNode(true);
  		// Obtain references to all cloned options
  		var clonedOptions = clone.getElementsByTagName("option");
  		// Onload init: call a generic function to display the related options in the dynamic select box
  		refreshDynamicSelectOptions(sel1, sel2, clonedOptions);
  		// Onchange of the main select box: call a generic function to display the related options in the dynamic select box
  		sel1.onchange = function() {
   			refreshDynamicSelectOptions(sel1, sel2, clonedOptions);
  		};
 	}
}

function refreshDynamicSelectOptions(sel1, sel2, clonedOptions) {
 	// Delete all options of the dynamic select box
 	while (sel2.options.length) {
  		sel2.remove(0);
 	}
 	// Create regular expression objects for "select" and the value of the selected option of the main select box as class names
 	var pattern1 = /( |^)(select)( |$)/;
 	var pattern2 = new RegExp("( |^)(" + sel1.options[sel1.selectedIndex].title + ")( |$)");
 	// Iterate through all cloned options
 	for (var i = 0; i < clonedOptions.length; i++) {
  		// If the classname of a cloned option either equals "select" or equals the value of the selected option of the main select box
  		if (clonedOptions[i].title.match(pattern1) || clonedOptions[i].title.match(pattern2)) {
 	 		 // Clone the option from the hidden option pool and append it to the dynamic select box
  		 	sel2.appendChild(clonedOptions[i].cloneNode(true));
  		}
 	}
}