// 获取长度为len的随机字符串
function _getRandomString(len) {
    len = len || 32;
    var $chars = 'ABCDEFGHJKMNPQRSTWXYZabcdefhijkmnprstwxyz2345678'; // 默认去掉了容易混淆的字符oOLl,9gq,Vv,Uu,I1
    var maxPos = $chars.length;
    var pwd = '';
    for (i = 0; i < len; i++) {
        pwd += $chars.charAt(Math.floor(Math.random() * maxPos));
    }
    return pwd;
}

方法参考phpMyAdmin 首页 -> Change Password -> Generate password 功能，如下图