js鼠标点击图片实现随机变换图片的方法

<html>
<title>鼠标点击图片即可随机变换图片</title>
<body bgcolor="#fef4d9" OnLoad="swapPic()">
<center>
<SCRIPT LANGUAGE="JavaScript">
<!-- Begin
var rand1 = 0;
var useRand = 0;
images = new Array;
images[1] = new Image();
images[1].src = "images/m01.jpg";
images[2] = new Image();
images[2].src = "images/m02.jpg";
images[3] = new Image();
images[3].src = "images/m03.jpg";
images[4] = new Image();
images[4].src = "images/m04.jpg";
function swapPic() {
var imgnum = images.length - 1;
do {
var randnum = Math.random();
rand1 = Math.round((imgnum - 1) * randnum) + 1;
} while (rand1 == useRand);
useRand = rand1;
document.randimg.src = images[useRand].src;
}
// End -->
</script>
<a onClick="swapPic();">
<img name="randimg" src="images/m09.jpg">
</a>
<br>
<font face="Verdana" size="-2">click image to change
</center>
</body>
</html>