// JScript File
/*
use example:
<script type="text/javascript" src="<%= ResolveUrl("~/Scripts/TextboxLeftCharachters.js") %>">    
</script>
txtMessage.Attributes.Add("onkeydown", "return isMaxLength(event," + this.txtMessage.ClientID + ", " + maxLength + ", " + lblCharactersLeft.ClientID + ")");
*/
function isMaxLength(e, txtBox, maxLength, lblCharactersLeft)
    {                 
        if (event.keyCode==8)
        {
            if (txtBox.value.length > 0)
            {
                setCharactersLeft(txtBox.value.length-1, maxLength, lblCharactersLeft);
            }
            return true;
        }
        else
        {
            if(txtBox.value.length < maxLength)
            {
                setCharactersLeft(txtBox.value.length+1, maxLength, lblCharactersLeft);
                return true;
            }
            else
            {
                return false
            }
        }
    }
    
    function setCharactersLeft(length, maxLength, lblCharactersLeft)
    {      
        currentTextLength = maxLength - length;
        lblCharactersLeft.innerText = currentTextLength;
    }