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;

}

protected void Page_Load(object sender, EventArgs e)
        {
            Button1.Attributes.Add("onclick", "javascript: CheckForEmptyTextbox();");
        }

 function checkForNumeric(txtVal)
   {
       var len = txtVal.value.length;
       var charVal = 0;
     for (var i=0;i     {
         charVal = txtVal.value.charCodeAt(i);
         if (!((charVal >= 48 && charVal <= 57)))
       {
          alert("Only Numeric Values are Allowed");
          txtVal.value = '';
          txtVal.focus();
         return false;
       }
     }
     return true;
 }
input type="text" id="txtNumber" onchange='checkForNumeric(this)'

function AllowNumericValue(myevent)
{
 var charVal = (myevent.which) ? myevent.which : myevent.keyCode
   if (charVal > 31 && (charVal < 48 || charVal > 57))
   {
     return false;
   }
 return true;
}
input type="text" id="Text2" onkeypress="return AllowNumericCharacters(event)"

 function AllowCharacterOnly(myevent) 
  {
      var Val = (myevent.which) ? myevent.which : myevent.keyCode
      if ((Val > 64 && Val < 91) || (Val > 96 && Val < 123))
      {
          return true;
      }
      return false;
  } 
input type="text" id="txtString" onkeypress="return AllowCharacterOnly(event)" 

function Multiplication() 
  {
      var first = document.getElementById('input1');
      var second = document.getElementById('input2');
      var third;

      third.value = first.value * second.value;
  }
input type= "text" id="txtvalue2" onblur='Multiplication()'