jquery blur() function event only in the dialogue bo

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Ajax

jQuery

Hello Everyone!
Can you do this, that the .blur() function just only check the input field when the client clicked on the dialoque box? Now when I click anywhere inside the page, it check the input fields
This is my js code

$(document).ready(function(){ 
    $('#tempForm').dialog({
        draggable: false,
        height: "450",
        width: "600",
        resizable: false,
        closeOnEscape: false ,
        title: "Registration",
        buttons:{
            "SUBMIT" : function(){
                $('#tempForm').submit();
            }
        }
         
    }); 
    $('#txt_username').blur(function(){
        //  if($('#txt_username').val().length < 6 || $('#txt_username').val().length > 12)
        //  {
        //      alert('Username must be between 6 and 12 characters');
        //  }
        //  else
        // {
        $.post('http://localhost/Image2/index.php/welcome/checkUsername', 
        {
            "username":$('#txt_username').val()
            }, 
        function(data){
            if(data.username == 'true'){
                //    console.log(data.username);
                // alert(data.username);//itt kiirja hogy true az alert
                alert('Hasznalatban van a usernev');
            }else{
                alert('nincs hasznalatban');//ide sosem jon el
            //    alert(data.username);
            }
        // 
        // else{
                 
        //  alert('username ok use it');
        //   }
        }, 'json');
    // }
    });
});