How to implement debounce fn into jQuery keyup event?

Question

A calculation is based on user input, and criteria is to use keyup rather than change or blur.

The problem is that the code fires on every keystroke, and I need it to delay and fire only once after a 500ms timeout. My example below obviously doesn't work, fiddle attached.

I found David Walsh's dbounce function, but cannot figure out how to implement it.

jsFiddle

HTML:

<input type="text" />
<input type="text" id="n2" class="num" value="17" disabled />
<input type="text" id="n3" class="num" value="32" disabled />

javascript/jQuery:

$('input').keyup(function(){
    var $this=$(this);
    setTimeout(function(){
        var n1 = $this.val();
        var n2 = $('#n2').val();
        var n3 = $('#n3').val();
        var calc = n1 * n2 * n3;
        alert(calc);
    },500);
});

//http://davidwalsh.name/javascript-debounce-function
function debounce(func, wait, immediate) {
    var timeout;
    return function() {
        var context = this, args = arguments;
        var later = function() {
            timeout = null;
            if (!immediate) func.apply(context, args);
        };
        var callNow = immediate && !timeout;
        clearTimeout(timeout);
        timeout = setTimeout(later, wait);
        if (callNow) func.apply(context, args);
    };
};

Answer 1

Use it like this:-

$('input').keyup(debounce(function(){
    var $this=$(this);
    //alert( $this.val() );
    var n1 = $this.val();
    var n2 = $('#n2').val();
    var n3 = $('#n3').val();
    var calc = n1 * n2 * n3;
    alert(calc);
},500));

Fiddle