<script language="javascript" type="text/javascript">
        /*
            Set maximum lengthe for textbox using JavaScript with remaining characters
            This function is used to validate the textbox for the Maximum lengh
            Parameter:
                txtBox --> This is the parameter to be passed as a textbox object
                maxLength --> This parameter is used to pass the Maximum length of the Textbox 
            ------------------------------------------------------------------------------------ 
            We have to call this function for onkeyup and onkeydown events of the textbox or textArea
        */
        function fnClicked(txtBox, maxLength)
        {
            //Here we are validating the Length of the Text. 
            //If the text is greater than the provided lenth, we have to ignore the last characters
            if(txtBox.value.length >= maxLength)
            {
               //Removing the last characters which are more than the length
               txtBox.value = txtBox.value.substring(0, 160);
            }
            //Displaying the Remaining characters
            document.getElementById('lbl').innerHTML = maxLength - txtBox.value.length;
        }
    </script>