asp.net - Alert the user if value exists in database after user leaves textbox -

i have textbox on form. when user leaves textbox, he/she informed value he/she entered exists. values stored in sql server database.
i have found similar here.

it works ok, causes postback.

here did.
first added onblur on aspx textbox function call. like:

 <asp:textbox id="id" onblur="myfunction()" <br/> 

in javascript added function:

function myfunction() {     var id= document.getelementbyid('textboxid').value;     if (parseint(id)) {         pagemethods.functionincodebehind(klid,success,failure);     } function success(response) {     alert ('success'); } function failure (response) {     alert('failure'); } 

in code behind created function:

<system.web.services.webmethod()> _ public shared function functionincodebehind(byval bo integer) integer   dim integer            ' stuff return   return  end function 

it works.