js实现键盘控制DIV移动的方法

<style type="text/css">
html,body{overflow:hidden;}
body{margin:0;padding:0;}
pre{color:green;padding:10px 15px;background:#f0f0f0;border:1px dotted #333;font:12px/1.5 Courier New;margin:12px;}
span{color:#999;}
#box{position:absolute;top:50px;left:300px;width:100px;height:100px;background:red;}
</style>

<script type="text/javascript">
window.onload = function ()
{
var oBox = document.getElementById("box");
var bLeft = bTop = bRight = bBottom = bCtrlKey = false;

setInterval(function ()
{
if (bLeft)
{
oBox.style.left = oBox.offsetLeft - 10 + "px"
}
else if (bRight)
{
oBox.style.left = oBox.offsetLeft + 10 + "px"
}

if (bTop)
{
oBox.style.top = oBox.offsetTop - 10 + "px" 
}
else if(bBottom)
{
oBox.style.top = oBox.offsetTop + 10 + "px"
}
//防止溢出
limit();
},30); 

document.onkeydown = function (event)
{
var event = event || window.event;
bCtrlKey = event.ctrlKey;

switch (event.keyCode)
{
case 37:
bLeft = true;
break;
case 38:
if(bCtrlKey)
{
var oldWidth = oBox.offsetWidth;
var oldHeight = oBox.offsetHeight;

oBox.style.width = oBox.offsetWidth * 1.5 + "px";
oBox.style.height = oBox.offsetHeight * 1.5 + "px"; 

oBox.style.left = oBox.offsetLeft - (oBox.offsetWidth - oldWidth) / 2 + "px";
oBox.style.top = oBox.offsetTop - (oBox.offsetHeight - oldHeight) / 2 + "px";

break; 
}
bTop = true;
break;
case 39:
bRight = true;
break;
case 40:
if(bCtrlKey)
{
var oldWidth = oBox.offsetWidth;
var oldHeight = oBox.offsetHeight;

oBox.style.width = oBox.offsetWidth * 0.75 + "px";
oBox.style.height = oBox.offsetHeight * 0.75 + "px"; 

oBox.style.left = oBox.offsetLeft - (oBox.offsetWidth - oldWidth) / 2 + "px";
oBox.style.top = oBox.offsetTop - (oBox.offsetHeight - oldHeight) / 2 + "px";

break; 
}
bBottom = true;
break;
case 49:
bCtrlKey && (oBox.style.background = "green");
break;
case 50:
bCtrlKey && (oBox.style.background = "yellow");
break;
case 51:
bCtrlKey && (oBox.style.background = "blue");
break;
}

return false
};

document.onkeyup = function (event)
{
switch ((event || window.event).keyCode)
{
case 37:
bLeft = false;
break;
case 38:
bTop = false;
break;
case 39:
bRight = false;
break;
case 40:
bBottom = false;
break;
}
};

//防止溢出
function limit()
{
var doc = [document.documentElement.clientWidth, document.documentElement.clientHeight]
//防止左侧溢出
oBox.offsetLeft <=0 && (oBox.style.left = 0);
//防止顶部溢出
oBox.offsetTop <=0 && (oBox.style.top = 0);
//防止右侧溢出
doc[0] - oBox.offsetLeft - oBox.offsetWidth <= 0 && (oBox.style.left = doc[0] - oBox.offsetWidth + "px");
//防止底部溢出
doc[1] - oBox.offsetTop - oBox.offsetHeight <= 0 && (oBox.style.top = doc[1] - oBox.offsetHeight + "px")
}
};
</script>

被移动的方块【DIV】
<div id="box"></div>