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// ===================================================================
// Author: Matt Kruse <>
// WWW:
// NOTICE: You may use this code for any purpose, commercial or
// private, without any further permission from the author. You may
// remove this notice from your final code if you wish, however it is
// appreciated by the author if at least my web site address is kept.
// You may *NOT* re-distribute this code in any way except through its
// use. That means, you can include it in your product, or your web
// site, or any other form where the code is actually being used. You
// may not put the plain javascript up on your site for download or
// include it in your javascript libraries for download. 
// If you wish to share this code with others, please just point them
// to the URL instead.
// Please DO NOT link directly to my .js files from your site. Copy
// the files to your server and use them there. Thank you.
// ===================================================================

// ------------------------------------------------------------------
// February 29, 2004: Fixed bug caused by LAST update, when control
//    checkbox is the first on checked. I hate when that happens.
// January 28, 2004: Fixed bug that occurred when checkbox was CHECKED
//    by default.
// December 16, 2002: Created
Original coding done by David Rogers -

DESCRIPTION: This library lets you quickly and easily make multiple checkboxes
behave as a group by limiting the total number of boxes that can be checked
and/or have a master control checkbox. 

COMPATABILITY: Should work on all Javascript-compliant browsers.

// Create a new CheckBoxGroup object
var myOptions = new CheckBoxGroup();

// Tell the object which checkboxes exist in your group. You may make multiple
// calls to this function, and/or pass multiple arguments. You may specify
// field names exactly, or use a wildcard at the beginning or end of the 
// name.

// Optionally set a "control" box which will effect all other boxes.

// Specify how your control box will interact with the group. Options are
// either "some" or "all" ("all" is default).
// all: Checking the box will select all the other boxes. Unchecking it will
//      uncheck all the group checkboxes. Selecting all the checkboxes in
//      the group will automatically check the control box.
// some: Checking any checkbox in the group will check the control box. The
//       control box may not be unchecked if any option in the group is 
//       still checked. If no boxes in the group are checked, you may still
//       check the control box.

// Optionally set the maximum number of boxes in the group which are allowed
// to be checked. You may pass a second argument which is an alert message to
// be displayed to the user if they exceed this limit.
myOptions.setMaxAllowed(3,"You may only select 3 choices!");

// IMPORTANT: After defining the group and behavior, you must insert an action
// into EVERY checkbox's onClick event-handler. Just specify the name of the
// group object that the checkbox belongs to, and pass it 'this' as the argument.
<INPUT TYPE="checkbox" NAME="cb1" onClick="myOptions.check(this)">

// That's it! Your checkboxes will now behave as a group!

function CheckBoxGroup() {
	this.checkboxWildcardNames=new Array();
	this.checkboxNames=new Array();
	// Public methods
	this.setMasterBehavior=CBG_setMasterBehavior;	// all, some
	// Private methods

// Set the master control checkbox name
function CBG_setControlBox(name) { this.controlBox=name; }

// Set the maximum number of checked boxes in the set, and optionally
// the message to popup when the max is reached.
function CBG_setMaxAllowed(num,msg) {
	if (msg!=null&&msg!="") { this.maxAllowedMessage=msg; }

// Set the behavior for the checkbox group master checkbox
//	All: all boxes must be checked for the master to be checked
//	Some: one or more of the boxes can be checked for the master to be checked
function CBG_setMasterBehavior(b) { this.masterBehavior = b.toLowerCase(); }

// Add checkbox wildcards to the checkboxes array
function CBG_addToGroup() {
	if (arguments.length>0) {
		for (var i=0;i<arguments.length;i++) {

// Expand the wildcard checkbox names given in the addToGroup method
function CBG_expandWildcards() {
	if (this.formRef==null) {alert("ERROR: No form element has been passed.  Cannot extract form name!"); return false; }
	for (var i=0; i<this.checkboxWildcardNames.length;i++) {
		var n = this.checkboxWildcardNames[i];
		var el = this.formRef[n];
		if (n.indexOf("*")!=-1) { this.addWildcardCheckboxes(n); }
		else if(CBG_nameIsArray(el)) { this.addArrayCheckboxes(n); }
		else { this.addSingleCheckbox(el); }

// Add checkboxes to the group which match a pattern
function CBG_addWildcardCheckboxes(name) {
	var i=name.indexOf("*");
	if ((i==0) || (i==name.length-1)) {
		searchString= (i)?name.substring(0,name.length-1):name.substring(1,name.length);
		for (var j=0;j<this.formRef.length;j++) {
			currentElement = this.formRef.elements[j];;
			var partialName = (i)?currentElementName.substring(0,searchString.length) : currentElementName.substring(currentElementName.length-searchString.length,currentElementName.length);
			if (partialName==searchString) {
				if(CBG_nameIsArray(currentElement)) this.addArrayCheckboxes(currentElement);
				else this.addSingleCheckbox(currentElement);

// Add checkboxes to the group which all have the same name
function CBG_addArrayCheckboxes(name) {
	if((CBG_nameIsArray(this.formRef[name])) && (this.formRef[name].length>0)) {
		for (var i=0; i<this.formRef[name].length; i++) { this.addSingleCheckbox(this.formRef[name][i]); }

function CBG_addSingleCheckbox(obj) {
	if (obj != this.formRef[this.controlBox]) {
		if (obj.checked) {

// Runs whenever a checkbox in the group is clicked
function CBG_check(obj) {
	var checked=obj.checked;
	if (this.formRef==null) {
		if (this.controlBox==null ||!=this.controlBox) {
			this.totalSelected += (checked)?-1:1;
	if (this.controlBox!=null&& {
		if (this.masterBehavior=="all") {
			for (i=0;i<this.checkboxNames.length;i++) { this.checkboxNames[i].checked=checked; }
		else {
			if (!checked) {
				obj.checked = (this.totalSelected>0)?true:false;
	else {
		if (this.masterBehavior=="all") {
			if (!checked) {
			else { this.totalSelected++; }
			if (this.controlBox!=null) {
		else {
			if (!obj.checked) { this.totalSelected--; }	
			else { this.totalSelected++; }
			if (this.controlBox!=null) {
			if (this.maxAllowed!=null) {
				if (this.totalSelected>this.maxAllowed) {
					if (this.maxAllowedMessage!=null) { alert(this.maxAllowedMessage); }
					return false;

function CBG_nameIsArray(obj) {
	return ((typeof obj.type!="string")&&(obj.length>0)&&(obj[0]!=null)&&(obj[0].type=="checkbox"));