JQ元素上移(互换位置)

js代码

function move_up(that)
{
    var a = that.parent('li').prev();
    var b = that.parent('li');
    if (a.length >= 1) {
    console.log(a.length);
    b.insertBefore(a);
}

html代码

<li>
    <a href="javascript:;" onclick="move_up($(this))">上移</a>
</li>
<li>
    <a href="javascript:;" onclick="move_up($(this))">上移</a>
</li>