js生成div

<div id="box">
    <!--<div>1</div>-->
</div>

*{
    margin: 0;
    padding: 0;    
}
#box{
    width: 500px;
    height: 500px;
    margin: 20px auto 0;
    position: relative;
}
#box div{
    width: 30px;
    height: 30px;
    text-align: center;
    line-height: 30px;
    color: #fff;
    font-weight: bold;
    font-size: 16px;
    position: absolute;
}

var oBox=document.getElementById("box");
var arr_color=["darkmagenta","darkgreen","darkcyan","palegreen","plum","deeppink","deepskyblue"];
var str="";

//left计算：i%10*40
//top计算通过向下取整：Math.floor(i/10)*40

for (var i=0;i<100;i++) {
    str+="<div style=‘left:"+i%10*40+"px;top:"+Math.floor(i/10)*40+"px;background:"+arr_color[i%6]+";‘>"+i+"</div>";
            }
oBox.innerHTML=str;