Question

    $check = "";

    $.ajax({
        url: "check.php",
        type: "POST",
        cache: false,
        data: $name + "=" + $value,
        success: function(data){
            $check = data;
            alert($check);
        }
    });

    alert($check);

The first msg is “Hello”

The second msg is “” Why ?

Answer 1

$.ajax is an asynchronous function, it returns immediately and calls the success callback when the success response is received.

Therefore, When the alert($check) at the bottom of your code is executed, the value of $check is not yet modified by the callback of ajax. That’s why you see the empty string.