อยากถามเกี่ยวกับ jquery check username availability

<script type="text/javascript">

$(document).ready(function() {
	$('#Loading').hide();    
});

function check_username(){

	var username = $("#username").val();
	if(username.length > 2){
		$('#Loading').show();
		$.post("<?php echo base_url();?>check.php", {
			username: $('#username').val(),
		}, function(response){
			$('#Info').fadeOut();
			 $('#Loading').hide();
			setTimeout("finishAjax('Info', '"+escape(response)+"')", 450);
		});
		return false;
	}
}

function finishAjax(id, response){
 
  $('#'+id).html(unescape(response));
  $('#'+id).fadeIn(1000);
} 

</script>



<script>
//-----------------Jquery form Validate-----------------------//
$(document).ready(function(){
	//global vars
	var form = $("#form1");
	
	var username = $("#username");
	var usernameInfo = $("#usernameInfo");
	
	var password = $("#password");
	var passwordInfo = $("#passwordInfo");
	
	var confirm_pass = $("#confirm_pass");
	var confirm_passInfo = $("#confirm_passInfo");
	
	var email = $("#email");
	var emailInfo = $("#emailInfo");
	
	var citizen_id = $("#citizen_id");
	var citizen_idInfo = $("#citizen_idInfo");
	
	var prefix_name = $("#prefix_name");
	var prefix_nameInfo = $("#prefix_nameInfo");
	
	var firstname = $("#firstname");
	var firstnameInfo = $("#firstnameInfo");
	
	var lastname = $("#lastname");
	var lastnameInfo = $("#lastnameInfo");
	
	var birthday = $("#birthday");
	var birthdayInfo = $("#birthdayInfo");
	
	var mobile_phone = $("#mobile_phone");
	var mobile_phoneInfo = $("#mobile_phoneInfo");
	
	var address = $("#address");
	
	//On blur
	username.blur(validateUsername);
	password.blur(validatePassword);
	confirm_pass.blur(validateConfirm_Pass);
	email.blur(validateEmail);
	citizen_id.blur(validateCitizen_Id);
	prefix_name.blur(validatePrefix_Name);
	firstname.blur(validateFirstname);
	lastname.blur(validateLastname);
	birthday.blur(validateBirthday);
	mobile_phone.blur(validateMobile_Phone);
	//On key press
	username.keyup(validateUsername);
	password.keyup(validatePassword);
	confirm_pass.keyup(validateConfirm_Pass);
	email.keyup(validateEmail);
	citizen_id.keyup(validateCitizen_Id);
	prefix_name.keyup(validatePrefix_Name);
	firstname.keyup(validateFirstname);
	lastname.keyup(validateLastname);
	birthday.keyup(validateBirthday);
	mobile_phone.keyup(validateMobile_Phone);
	//On Submitting
	form.submit(function(){
		if(validateUsername() & validateEmail() & validatePassword() & validateConfirm_Pass() & validateCitizen_Id() & validatePrefix_Name() & validateFirstname() & validateLastname() & validateBirthday() & validateMobile_Phone())
			return true
		else
			return false;
	});
	
	//validation functions
	function validateEmail(){
		//testing regular expression
		var a = $("#email").val();
		var filter = /^[a-zA-Z0-9]+[a-zA-Z0-9_.-]+[a-zA-Z0-9_-]+@[a-zA-Z0-9]+[a-zA-Z0-9.-]+[a-zA-Z0-9]+.[a-z]{2,4}$/;
		//if it's valid email
		if(filter.test(a)){
			email.removeClass("error");
			emailInfo.html('&nbsp;<img src="<?php echo base_url();?>/images/correct.gif">');
			emailInfo.removeClass("error");
			return true;
		}
		//if it's NOT valid
		else{
			email.addClass("error");
			emailInfo.text("Stop cowboy! Type a valid e-mail please :P");
			emailInfo.addClass("error");
			return false;
		}
	}
	function validateUsername(){
		//if it's NOT valid
		if(username.val().length < 4){
			username.addClass("error");
			usernameInfo.text("คุณยังไม่ได้กรอก Username ใส่ตัวเลข-ตัวอักษร 4 ตัวขึ้นไป");
			usernameInfo.addClass("error");
			return false;
		}
		//if it's valid
		else{
			username.removeClass("error");
			usernameInfo.html('&nbsp;<img src="<?php echo base_url();?>/images/correct.gif">');
			usernameInfo.removeClass("error");
			return true;
		}
	}
	function validatePassword(){
		var a = $("#password");
		var b = $("#confirm_pass");

		//it's NOT valid
		if(password.val().length <5){
			password.addClass("error");
			passwordInfo.text("คุณยังไม่ได้กรอก Password ใส่ตัวเลข-ตัวอักษร 5 ตัวขึ้นไป");
			passwordInfo.addClass("error");
			return false;
		}
		//it's valid
		else{			
			password.removeClass("error");
			passwordInfo.html('&nbsp;<img src="<?php echo base_url();?>/images/correct.gif">');
			passwordInfo.removeClass("error");
			
			return true;
		}
	}
	function validateConfirm_Pass(){
		var a = $("#password");
		var b = $("#confirm_pass");
		//are NOT valid
		if( password.val() != confirm_pass.val() ){
			confirm_pass.addClass("error");
			confirm_passInfo.text("คุณกรอก Password ไม่ตรงกัน!");
			confirm_passInfo.addClass("error");
			return false;
		}
		//are valid
		else{
			confirm_pass.removeClass("error");
			confirm_passInfo.html('&nbsp;<img src="<?php echo base_url();?>/images/correct.gif">');
			confirm_passInfo.removeClass("error");
			return true;
		}
	}
	function validateCitizen_Id(){
		if(citizen_id.val().length < 17){
			citizen_id.addClass("error");
			citizen_idInfo.text("คุณยังไม่ได้ กรอก รหัสบัตรประชาชน");
			citizen_idInfo.addClass("error");
			return false;
		}
		else{
			citizen_id.removeClass("error");
			citizen_idInfo.html('&nbsp;<img src="<?php echo base_url();?>/images/correct.gif">');
			citizen_idInfo.removeClass("error");
			return true;
		}
	}
	function validatePrefix_Name(){
		if(prefix_name.val().length < 1){
			prefix_name.addClass("error");
			prefix_nameInfo.text("คุณยังไม่ได้ เลือก คำนำหน้าชื่อ");
			prefix_nameInfo.addClass("error");
			return false;
		}
		else{
			prefix_name.removeClass("error");
			prefix_nameInfo.text("success");
			prefix_nameInfo.removeClass("error");
			return true;
		}
	}
	function validateFirstname(){
		if(firstname.val().length < 1){
			firstname.addClass("error");
			firstnameInfo.text("คุณยังไม่ได้ กรอก ชื่อ");
			firstnameInfo.addClass("error");
			return false;
		}
		else{
			firstname.removeClass("error");
			firstnameInfo.text("success");
			firstnameInfo.removeClass("error");
			return true;
		}
	}
	function validateLastname(){
		if(lastname.val().length < 1){
			lastname.addClass("error")
			lastnameInfo.text("คุณยังไม่ได้ กรอก นามสกุล");
			lastnameInfo.addClass("error");
			return false;
		}
		else{
			lastname.removeClass("error");
			lastnameInfo.text("success");
			lastnameInfo.removeClass("error");
			return true;	
		}
	}
	function validateBirthday(){
		if(birthday.val().length < 10){
			birthday.addClass("error");
			birthdayInfo.text("คุณยังไม่ได้ เลือก วัน เดือน ปีเกิดของคุณ");
			birthdayInfo.addClass("error");
			return false;
		}
		else{
			birthday.removeClass("error");
			birthdayInfo.text("success");
			birthdayInfo.removeClass("error");
			return true;
		}
	}
	function validateMobile_Phone(){
		if(mobile_phone.val().length < 10){
			mobile_phone.addClass("error");
			mobile_phoneInfo.text("คุณยังไม่ได้ กรอก เบอร์โทรศัพท์");
			mobile_phoneInfo.addClass("error");
			return false;
		}
		else{
			mobile_phone.removeClass("error");
			mobile_phoneInfo.text("success");
			mobile_phoneInfo.removeClass("error");
			return true;
		}
	}
});
//-----------------End Jquery form Validate-----------------------//
</script>