<script type="text/javascript">
function openKCFinder(field) {
    window.KCFinder = {
        callBack: function(url) {
            field.value = url;
            window.KCFinder = null;
        }
    };
    window.open('/demo/kcfinder/browse.php?type=files&dir=files/public', 'kcfinder_textbox',
        'status=0, toolbar=0, location=0, menubar=0, directories=0, ' +
        'resizable=1, scrollbars=0, width=800, height=600'
    );
}
</script>

Selected file:
<input type="text" readonly="readonly" onclick="openKCFinder(this)"
    value="Click here and select a file double clicking on it" style="width:600px;cursor:pointer" />