Edit in JSFiddle

<div class="left">
     <h3>Tanpa Debounce</h3>

    <div class="box" id="box-1">Gerakan pointer mouse di sini...</div>
</div>
<div class="right">
     <h3>Dengan Debounce</h3>

    <div class="box" id="box-2">Gerakan pointer mouse di sini...</div>
</div>
<div style="clear:both;"></div>

var elem_1 = document.getElementById('box-1'),
    elem_2 = document.getElementById('box-2');

// Tanpa debounce
elem_1.onmousemove = function () {
    this.innerHTML += ' test!';
};

// Dengan debounce
var timer = null;
elem_2.onmousemove = function () {
    if (timer) clearTimeout(timer);
    timer = setTimeout(function () {
        elem_2.innerHTML += ' test!';
        timer = null;
    }, 300);
};