点击button1让button1移到button2后边，代码如何写呢，请各位大神赐教？？？

"让button1移到button2后边”，这个如何理解？意思是让button2覆盖掉button1？

<script>
    var btn1 = document.getElementById('button1');
    btn1.onclick=function(){
        var part = document.getElementById('parbut');
        var btn2 = document.getElementById('button2');
        parbut.insertBefore(btn2, this);
    }
</script>