Javascript code for checking null value in Textbox.


function CheckForEmptyTextbox()
{
var s;
var txtValue;
txtValue = document.getElementById('TextBox1');
if (txtValue.value == '')
{
s = confirm('TextBox1 is blank, do you want to continue?');
return s;
}
return true;

}

Button1.Attributes.Add("onclick", "javascript: CheckForEmptyTextbox();");