What does this construct (x = x || y) mean?
<p>Iam debugging some javascript, and cant explain what this "||" does?</p>

<pre><code>  loadingError: function(title, msg){
        var title   = title || 'Error';
        var msg     = msg || 'Error on Request';

        new my.widget.InformationBox({
            title: title,
            message: msg,
            type: 'error'
        }).show();
    }
</code></pre>

<p>Can someone give me an hint, why this guy is using var title = title || 'ERROR' ??</p>
