javascript - What is the correct way to call a validation Jscript function when there is a DB call? -

sorry if title doesn't explain much.

i have page textbox, button , error message.

i need validate if text entered in textbox not null or empty, has length, there no weird characters in , last not least, username doesn't exists in database. part done , working.

my question is, what's best way call jscript function validate asp:textbox username type.

right see 3 different ways.

1. using .blur call when focus lost on textbox

2. using .keyup or .keydown call whenever key pressed

3. using timer validate every x seconds

now problem .blur doesn't validate without loosing focus on thing worth of focus on page. problem .keyup , .keydown call db way many times. , problem timer i'm not sure if there problem timer, why i'm asking.

i have validation server side cannot go throught.

for more information, here jscript .blur have right now.

<script type="text/javascript"> var name; var namevalid = false;  $(document).ready(function () {     name = $("#txtbox");     validatename();     name.blur(function () {         validatename();     });  });  function validatename() {     namevalid = false;     pagemethods.namevalidmethod(name.val(), successname, error); }; 

what best way it?

edit: add more information. right page textbox , button. in future when update website i'll have more textbox in page.

for short forms, best user experience perform validation upon submission of form. opposed having button and/or relying on user hit 'enter' key?

then following validation done javascript on submission of form: "if text entered in textbox not null or empty, has length, there no weird characters in it"

then if of pass, continue submission server check uniqueness of username.