Mask TextBox ASP.NET Control

function MaskTextBox(document, textBoxId, hiddenMaskId)
{
	//Expose members
	this.onKeyUp = onKeyUp;
	this.onBlur = onBlur;
	this.setCaretPos = setCaretPos;
	//Members
	var prev = "";
	var caretPos = 0;
	var start = 0;
	var end = 0;
	var maxLen = 0;
	var textBox = document.getElementById(textBoxId);
	if (textBox != null)
		maxLen = textBox.getAttribute("maxlength");
	var arr;
	var sepIndexArray;
	var sepRemoveRegEx;
	var hiddenMask = document.getElementById(hiddenMaskId);
	if (hiddenMask != null)
	{
		arr = hiddenMask.value.split("||");
		if (arr != null && arr.length == 2)
		{
			sepIndexArray = arr[0].split("|");
			sepRemoveRegEx = new RegExp(arr[1], "g");
		}
	}
	function onBlur(o, e)
	{
		o.value = reformat(o.value, maxLen);
	}
	function onKeyUp(o)
	{
		var ret = setCaretPos(o);
		if (o.value != prev)
		{
			o.value = reformat(o.value, maxLen);
			caretPos = offsetCarretPos(o);
			prev = o.value;
			setRange(o, caretPos);
			ret = setCaretPos(o);
		}
		return ret;
	}
	function reformat(val, len)
	{
		val = insertSeparators(removeSeparators(val));
		if (val.length > len)
			val = val.substr(0, len);
		return val;
	}
	function insertSeparators(val)
	{
		var sep, sepIndexPair, sepIndex = 0;
		for (var i = 0; i < sepIndexArray.length; ++i)
		{
			sepIndexPair = sepIndexArray[i].split("!");
			sepIndex = sepIndexPair[1];
			if (val.length > sepIndex)
			{
				sep = sepIndexPair[0];
				if (sep != val.substr(sepIndex, 1))
					val = val.substr(0, sepIndex) + sep + val.substr(sepIndex, val.length - sepIndex);
			}
			else
				break;
		}
		return val;
	}
	function removeSeparators(val)
	{
		return val.replace(sepRemoveRegEx, "");
	}
	function offsetCarretPos(o)
	{
		var caret = caretPos;
		var offset = 0;
		var valLen = o.value.length
		var prevLen = prev.length
		if (valLen > prevLen)
		{
			if (caret > prevLen)
				caret = valLen;
			else
			{
				var sep;
				for (var i = 0; i < sepIndexArray.length; ++i)
				{
					sepIndexPair = sepIndexArray[i].split("!");
					sep = sepIndexPair[0];
					if (o.value.substr(caretPos + offset - 1, 1) == sep)
					{
						offset = (valLen - prevLen) > 1 ? 1 : 0;
						offset = offset + 1;
					}
				}
				offset = (offset > -1 ? offset : 0);
			}
		}
		return caret + offset;
	}
	function setRange(o)
	{
		if (o.value.length > 0)
		{
			if (o.createTextRange)
			{
				var txRange = o.createTextRange();
				txRange.move("character", caretPos);
				txRange.select();
			}
			else o.setSelectionRange(caretPos, caretPos);
		}
	}
	function trimCaretPos()
	{
		if (caretPos < 0) caretPos = 0;
		else if (caretPos > maxLen) caretPos = maxLen;
	}
	//Based on Diego Perini <dperini@nwbox.com> sample >>>
	function setCaretPos(o)
	{
		var s = getSelStart(o), e = getSelEnd(o);
		if (s == start && e == end)
			return false;
		caretPos = s;
		start = s;
		end = e;
		return true;
	}
	function getSelStart(o)
	{
		if (o.createTextRange)
		{
			var r = document.selection.createRange().duplicate();
			r.moveEnd('character', o.value.length);
			if (r.text == '')
				return o.value.length;
			return o.value.lastIndexOf(r.text);
		}
		else return o.selectionStart;
	}
	function getSelEnd(o)
	{
		if (o.createTextRange)
		{
			var r = document.selection.createRange().duplicate();
			r.moveStart('character', -o.value.length);
			return r.text.length;
		}
		else return o.selectionEnd;
	}
	//<<<
}