js实现图片放大缩小

<script language="javascript">
    var oTime;
    function chgSize(args) {
        var oImg = document.all['oImg'];
        oImg.style.zoom = parseInt(oImg.style.zoom) + (args ? +1 : -1)  + '%';
        oTime = window.setTimeout('chgSize(' + args + ')', 100);
    }    
</script>
<div style="height: 200px; overflow: auto;">
<img id="oImg" src="/images/global_top_logo.gif" style="zoom: 100%;">
</div>
<button onmousedown="chgSize(true);" onmouseup="window.clearTimeout(oTime);">&uarr;</button>
<button onmousedown="chgSize(false);" onmouseup="window.clearTimeout(oTime);">&darr;</button>