var reOneOrMoreDigits = /[\d+]/;
var reNoDigits = /[^\d]/gi;

function doMask(event, textBox) 
{
	var keyCode = event.which ? event.which : event.keyCode;
	// enter, backspace, delete and tab keys are allowed thru
	if(keyCode == 13 || keyCode == 8 || keyCode == 9 || keyCode == 46)
		return true;

	// get character from keyCode
	var keyCharacter = cleanKeyCode(keyCode);

	var val = textBox.value;
	var mask = '(###) ###-####';

	// simple Regex to check if key is a digit
	if(reOneOrMoreDigits.test(keyCharacter) == false)
		return false;

	// get value minus any masking by removing all non-numerics
	val = val.replace(reNoDigits,'');			

	val += keyCharacter;

	// mask it...val holds the existing TextBox.value + the current keystroke
	textBox.value = val.maskValue(mask);

	setCaretAtEnd(textBox);

	return false;
}

function onFocusMask(textBox) 
{
	var val = textBox.value;
	var mask = '(###) ###-####';
	if(val.length == 0 || val == null) {
		var i = mask.indexOf('#');
		textBox.value = mask.substring(0,i);
	}
	setCaretAtEnd(textBox);

	textBox.maxlength = mask.length;
}

function onBlurMask(textBox) 
{
	var val = textBox.value;

	// if no digits blank it out.
	if(reOneOrMoreDigits.test(val) == false) {
		textBox.value = '';
	}
}

String.prototype.maskValue = function(mask) 
{
	var retVal = mask;
	var val = this;

	//loop thru mask and replace #'s with current value one at a time
	for(var i=0;i<val.length;i++) {
		retVal = retVal.replace(/#/i, val.charAt(i));
	}

	// remove the rest of #'s
	retVal = retVal.replace(/#/gi, "");
	return retVal;
}

// numeric keypad returns keyCodes that are not workable
// keypad '1' returns keyCode 97 which String.fromCharCode converts to an 'a'.

function cleanKeyCode(key)
{
	switch(key)
	{
		case 96: return "0"; break;
		case 97: return "1"; break;
		case 98: return "2"; break;
		case 99: return "3"; break;
		case 100: return "4"; break;
		case 101: return "5"; break;
		case 102: return "6"; break;
		case 103: return "7"; break;
		case 104: return "8"; break;
		case 105: return "9"; break;
		default: return String.fromCharCode(key); break;
	}
}

// From:
// http://www.faqts.com/knowledge_base/view.phtml/aid/1159/fid/130
function setCaretAtEnd (field) 
{
  if (field.createTextRange) {
    var r = field.createTextRange();
    r.moveStart('character', field.value.length);
    r.collapse();
    r.select();
  }
}