99乘法表隔行变色

* {
            margin: 0;
            padding: 0;
        }

        span {
            display: inline-block;
            padding: 5px 8px;
        }
        li.bg0{
            background: lightgoldenrodyellow;
        }
        li.bg1{
            background: lightpink;
        }
        li.bg2{
            background: lightcyan;
        }
        li.bg3{
            background: linen;
        }
        li.changeBg{
            background: darkmagenta;
            color: white;
        }

var oUl = document.createElement("ul");
    var oLi = oUl.getElementsByTagName("li");
    var str = '';
    var oldBg = null;
    for (var i = 1; i <= 9; i++) {
        str += '<li>';
        for (var j = 1; j <= i; j++) {
            str += '<span>' + (j + '*' + i + '=' + j * i) + '</span>';
        }
        str += '</li>';
    }
    oUl.innerHTML=str;
    document.body.appendChild(oUl);
    for(var i=0;i<oLi.length;i++){
        oLi[i].className='bg'+i%4;
        oLi[i].onmouseover=function(){
            oldBg=this.className;
            this.className='changeBg';
        };
        oLi[i].onmouseout=function(){
            this.className=oldBg;
        }
    }