Good morning, I'm a little noob in js and I've made one script to validate a registration form.

The code works perfectly, but I know my code is not the best way to do it, so I'd like someone would read it and tell me where are my mistakes, so I can learn.

This is the "js" code.

Code:
//Sleep
function sleep(ms){
	var dt = new Date();
	dt.setTime(dt.getTime() + ms);
	while (new Date().getTime() < dt.getTime());
}

$(document).ready(function(){
	
	//Variables globales
	var usr = $("#username");
	var pass = $("#password");
	var cpass = $("#confirm_password");
	var email = $("#email");
	var b_usr = false;
	var b_pass = false;
	var b_cpass = false;
	var b_email = false;
	var b_agree = false;

	//Username Check
	function validateUsername(){

		usr = $("#username").val();
		if(usr.length >= 4)
		{

			$.ajax({  
			type: "POST",  
			url: "check.php",  
			data: "username="+ usr,  
			success: function(msg){  
		   
		   $("#status").ajaxComplete(function(event, request, settings){ 

			if(msg == 'OK')
			{ 
				$("#username").removeClass('object_error'); // if necessary
				$("#username").addClass("object_ok");
				$(this).html('&nbsp;<img src="tick.ico" align="absmiddle">');
				b_usr = true;
			}  
			else  
			{  
				$("#username").removeClass('object_ok'); // if necessary
				$("#username").addClass("object_error");
				$(this).html(msg);
				b_usr = false;
			}  
		   
		   });

		 } 
		   
		  }); 

		}else{
			$("#status").html('<p style="color:white; font-size:14px; text-align:center; padding:5px; background-color:rgba(255,0,0,0.3);">The username should have at least 4 characters.</p>');
			$("#username").removeClass('object_ok'); // if necessary
			$("#username").addClass("object_error");
			b_usr = false;
		}

	}
	
	//Password check
	function validatePassword() { 

		pass = $("#password").val();
		
		if(pass.length >= 6){
			$("#status2").html('&nbsp;<img src="tick.ico" align="absmiddle">');
			b_pass = true;
		}else{
			$("#status2").html('<p style="color:white; font-size:14px; text-align:center; padding:5px; background-color:rgba(255,0,0,0.3);">Your password must have at least 6 characters</p>');
			$("#password").removeClass('object_ok'); // if necessary
			$("#password").addClass("object_error");
			b_pass = false;
		} 
	   
	}
	
	//Password confimation check
	function validatePassword2() { 

		cpass = $("#confirm_password").val();
		var pass = $("#password").val();
		if(cpass == pass){
			if(cpass.length >= 6){
				$("#status3").html('&nbsp;<img src="tick.ico" align="absmiddle">');
				b_cpass = true;
			}else{
				$("#status3").html('<p style="color:white; font-size:14px; text-align:center; padding:5px; background-color:rgba(255,0,0,0.3);">Your password must have at least 6 characters</p>');
				$("#confirm_password").removeClass('object_ok'); // if necessary
				$("#confirm_password").addClass("object_error");
				b_cpass = false;
			}
		}else{
			$("#status3").html('<p style="color:white; font-size:14px; text-align:center; padding:5px; background-color:rgba(255,0,0,0.3);">The passwords doesn`t match</p>');
			$("#confirm_password").removeClass('object_ok'); // if necessary
			$("#confirm_password").addClass("object_error");
			b_cpass = false;
		} 
	   
	}
	
	function validateEmail() { 

		email = $("#email").val();
		var mailformat = /^\w+([\.-]?\w+)*@\w+([\.-]?\w+)*(\.\w{2,3})+$/;
		
		if(email.match(mailformat)){

			$.ajax({  
				type: "POST",  
				url: "checkmail.php",  
				data: "email="+ email,  
				success: function(msg){  
			   
				   $("#status4").ajaxComplete(function(event, request, settings){ 

						if(msg == 'OK')
						{ 
							$("#email").removeClass('object_error'); // if necessary
							$("#email").addClass("object_ok");
							$(this).html('&nbsp;<img src="tick.ico" align="absmiddle">');
							b_email = true;
						}  
						else  
						{  
							$("#email").removeClass('object_ok'); // if necessary
							$("#email").addClass("object_error");
							$(this).html(msg);
							b_email = false;
						}  
				   
					});
				}
			});
		}else{
			$("#status4").html('<p style="color:white; font-size:14px; text-align:center; padding:5px; background-color:rgba(255,0,0,0.3);">The email you have entered is invalid</p>');
			$("#email").removeClass('object_ok'); // if necessary
			$("#email").addClass("object_error");
			b_email = false;
		} 
	   
	}
	
	//Validate checkbox
	$("#agree").change(function () { 
	
		if(document.form.agree.checked == true){
			$("#status7").html('');
			$("#agree").removeClass('object_error'); // if necessary
			$("#agree").addClass("object_ok");
			b_agree = true;
		}else{
			$("#status7").html('<p style="color:white; font-size:14px; text-align:center; padding:5px; background-color:rgba(255,0,0,0.3);">You must accept the agreement</p>');
			$("#agree").removeClass('object_ok'); // if necessary
			$("#agree").addClass("object_error");
			b_agree = false;
		}
	});

	
	//Validation on blur.
	usr.blur(validateUsername);
	pass.blur(validatePassword);
	cpass.blur(validatePassword2);
	email.blur(validateEmail);
	
	//Validation on submit.
	// Envio de formulario  
	$("#signupForm").submit(function(){
		validateUsername();
		validatePassword();
		validatePassword2();
		validateEmail();
		if(document.form.agree.checked == true){
			$("#status7").html('');
			$("#agree").removeClass('object_error'); // if necessary
			$("#agree").addClass("object_ok");
			b_agree = true;
		}else{
			$("#status7").html('<p style="color:white; font-size:14px; text-align:center; padding:5px; background-color:rgba(255,0,0,0.3);">You must accept the agreement</p>');
			$("#agree").removeClass('object_ok'); // if necessary
			$("#agree").addClass("object_error");
			b_agree = false;
		}
		sleep(2000);
		if(b_usr & b_pass & b_cpass & b_email & b_agree){
			return true;
		}
		else{
			return false;
		}
	});
	
});
These are the "php" codes called from the "js":

PHP Code:
<?php

// This is a sample code in case you wish to check the username from a mysql db table

if(isSet($_POST['username'])){

    
$username $_POST['username'];
    
$password $_POST['password'];
    
$truepass "";
    
$truenick "";

    
$dbHost 'localhost'// usually localhost
    
$dbUsername 'root';
    
$dbPassword '';
    
$dbDatabase 'supahsonic';

    
$db mysql_connect($dbHost$dbUsername$dbPassword) or die ("Unable to connect to Database Server.");
    
mysql_select_db ($dbDatabase$db) or die ("Could not select database.");

    
$cons="select user_nick, user_pass from user where user_nick='".$username."' AND user_pass='".$password."'";
    
$result=mysql_query($cons);
    while(
$fila=mysql_fetch_array($result)){
        
$truenick=$fila['user_nick'];
        
$truepass=$fila['user_pass'];
    }
    if(
$password==$truepass && $username==$truenick){
        echo 
'OK';
    }
}
?>
PHP Code:
<?php

// This is a sample code in case you wish to check the email from a mysql db table

if(isSet($_POST['email']))
{
$email $_POST['email'];

$dbHost 'localhost'// usually localhost
$dbemail 'root';
$dbPassword '';
$dbDatabase 'supahsonic';

$db mysql_connect($dbHost$dbemail$dbPassword) or die ("Unable to connect to Database Server.");
mysql_select_db ($dbDatabase$db) or die ("Could not select database.");

$sql_check mysql_query("select user_id from user where user_mail='".$email."'") or die(mysql_error());

if(
mysql_num_rows($sql_check))
{
echo 
'<p style="color:white; font-size:14px; text-align:center; padding:5px; background-color:rgba(255,0,0,0.3);">The email <STRONG>'.$email.'</STRONG> is already in use.</p>';
}
else
{
echo 
'OK';
}

}
?>
Thank you in advance.