<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>随机数</title>
</head>
<body>
<script type="text/javascript">
function Randnum(value){
var s=1000;
var d=500;
if(value=='b'){
document.write(s+parseInt(500*Math.random()));
}else{
document.write(d+parseInt(500*Math.random()));
}
}
</script>
<script>Randnum();</script>
</body>
</html>
效果图：