js随机数（随机密码）
1. Math.random()生成一个0~1的随机数 0<=Math.random()<1
2. Math.random()*100 则生成一个0~100之间的随机数
3. Math.random()*100 + 100 则生成一个100~200之间的随机数
4. 所以Math.random()*m 则生成一个0~m的随机数

//下面是一个生成随机字母(随机密码的JavaScript)
<hr />
<script type="text/javascript" language="javascript">
function randomPassword(size)
{
    var seed = new Array('A','B','C','D','E','F','G','H','I','J','K','L','M','N','P','Q','R','S','T','U','V','W','X','Y','Z',
                         'a','b','c','d','e','f','g','h','i','j','k','m','n','p','Q','r','s','t','u','v','w','x','y','z',
                         '2','3','4','5','6','7','8','9'
                         );//数组
    seedlength = seed.length;//数组长度
    var createPassword = '';
    for (i=0;i<size;i++) {
        j = Math.floor(Math.random()*seedlength);
        createPassword += seed[j];
    }
    return createPassword;
}
document.write(randomPassword(6));
</script>