走过路过不要错过，帮忙看下错在哪了

function get_previousSibling(n){

        var x=n.previousSibling;

        while(x && x.nodeType!=1)

        {x=x.previousSibling;}

        return x;

    }

    var x=document.getElementsByName("li");

    var y=x[x.length-1];

    document.write("<br/><br/>"+y.nodeName+"="+y.innerHTML+"<br/>"+"previousSibling:"+get_previousSibling(y).nodeName+get_previousSibling(y).innerHTML);