How to add randomness to the blink effect? : <p>JS</p>

<pre><code> &lt;script&gt;
        (function blink() { 
            $('.demo').fadeOut(500).fadeIn(400, blink); 
        })();
    &lt;/script&gt;
</code></pre>

<p>CSS</p>

<pre><code>.demo {
    background: url('../res/logo.png') no-repeat;
    width: 200px;
    height: 200px;
    margin-top: 355px;
    margin-left: 855px;
}
</code></pre>

<p>How do i add randomness to this blinking effect?</p>
