function generateRandomString(len) {
var randomString = "";
for (; randomString .length < len; randomString += Math.random().toString(36).substr(2));
return randomString.substr(0, len);
};
alert(generateRandomString(25));
201603061520_《Javascript生成随机字符串函数（可用于加密）》
原文：http://www.cnblogs.com/beesky520/p/5247569.html