怎样让一个矩形上下左右键盘移动

• w 87 a 65 s 83 d 68
• up 38 right 37 down 40 right 39

var obox = document.getElementsByTagName('div');

document.onkeydown = function(event){
    mover(event);
}

function mover(event){
    clearTimeout(timer);
    var evt = event || window.event;
    //console.log(evt.which || evt.keyCode)
    var speed =19;
    var timer = setTimeout(function(code){
        var code = evt.which || evt.keyCode;
        // clearInterval(timer);
        //console.log(code)
        // console.log(code)
        switch (code){
            case 87:obox[0].style.top = obox[0].offsetTop - speed + "px";break;
            case 65:obox[0].style.left = obox[0].offsetLeft -speed + "px";break;
            case 83:obox[0].style.top = obox[0].offsetTop + speed + "px";break;
            case 68:obox[0].style.left = obox[0].offsetLeft + speed + "px";break;

            case 38:obox[0].style.top = obox[0].offsetTop - speed + "px";break;
            case 37:obox[0].style.left = obox[0].offsetLeft -speed + "px";break;
            case 40:obox[0].style.top = obox[0].offsetTop + speed + "px";break;
            case 39:obox[0].style.left = obox[0].offsetLeft + speed + "px";break;
        }
    for(var i = obox.length - 1 ; i > 0 ; i --){
        obox[i].style.left = obox[i-1].offsetLeft + "px";
        obox[i].style.top = obox[i-1].offsetTop + "px";
        obox[i].style.background = randomColor();
    }

    },1)

}
function randomColor(){//随机颜色值
        var arr = [1,2,3,4,5,6,7,8,9,0,"A","B","C","D","E","F"];
        var res = "#";
        for(var i = 0 ; i < 6; i++){
            res += arr[parseInt(Math.random()*16)]
        }
        return res;

    }

// function getKey(event){//测试鼠标键值的函数
//     var evt = event || window.event;
//     console.log(evt.which || evt.keyCode)
//     return evt.which || evt.keyCode
// }