funtion fn(len){
let stringA = ‘abcd.....890‘;
let length = stringA.length;
let temp = ‘‘;
for(let i=0;i<len;i++){
temp += stringA.CharAt(Math.floor(Math.random( )*length));
}
return temp;
}
原文：https://www.cnblogs.com/sonsmart/p/15265665.html