How to use variable after jquery ajax function

Question

Help me please, how to get result from jquery function ?

$(document).ready(function(){
    $.ajax({
        url: "http://somemywebsite.com/getdata.php",
        type: 'GET',
        dataType: 'json',
        success: function(res) {
            $( "input[name*='fname']" ).val( res ); /// this code works, fname field was changed to my!
        }
    });


//but how i can get the result of code?
alert(res); /// Doesn't work, empy!

var test = $( "input[name*='fname']" ).val;

alert(test); //Doesn't work too

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>

All data got empty status ...