Math.random理解练习

<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>数学方法随机的运用</title>
</head>
<body>
<img src="" id="myimg">
<script>
    /*0<x<1;//x=Math.random();
    0<x*5<5;//x.length,0到5之间的浮点数；
    0<=Math.floor(x*5)<=4;//取得x的index;*/
    var arr=["a.png","b.png","c.png","d.png","e.png"];
    var rand=Math.random;
    var tot=arr.length;
    var index=Math.floor(rand*tot);

    var myImg=document.getElementById("myimg");
    myImg.src=arr[index];
</script>
</body>
</html>