Generate random string/characters in JavaScript

Question

I want a 5 character string composed of characters picked randomly from the set [a-zA-Z0-9].

What's the best way to do this with JavaScript?

Answer 1

To meet requirement [a-zA-Z0-9] and length=5 use

btoa(Math.random()).substr(5, 5);

Lowercase letters, uppercase letters, and numbers will occur.

Answer 2

I know everyone has got it right already, but i felt like having a go at this one in the most lightweight way possible(light on code, not CPU):

function rand(length, current) {
  current = current ? current : '';
  return length ? rand(--length, "0123456789ABCDEFGHIJKLMNOPQRSTUVWXTZabcdefghiklmnopqrstuvwxyz".charAt(Math.floor(Math.random() * 60)) + current) : current;
}

console.log(rand(5));

It takes a bit of time to wrap your head around, but I think it really shows how awesome javascript's syntax is.

Answer 3

In case anyone is interested in a one-liner (although not formatted as such for your convenience) that allocates the memory at once (but note that for small strings it really does not matter) here is how to do it:

Array.apply(0, Array(5)).map(function() {
    return (function(charset){
        return charset.charAt(Math.floor(Math.random() * charset.length))
    }('ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789'));
}).join('')

You can replace 5 by the length of the string you want. Thanks to @AriyaHidayat in this post for the solution to the map function not working on the sparse array created by Array(5).

Answer 4

Generate 10 characters long string. Length is set by parameter (default 10).

function random_string_generator(len) {
var len = len || 10;
var str = '';
var i = 0;

for(i=0; i<len; i++) {
    switch(Math.floor(Math.random()*3+1)) {
        case 1: // digit
            str += (Math.floor(Math.random()*9)).toString();
        break;

        case 2: // small letter
            str += String.fromCharCode(Math.floor(Math.random()*26) + 97); //'a'.charCodeAt(0));
        break;

        case 3: // big letter
            str += String.fromCharCode(Math.floor(Math.random()*26) + 65); //'A'.charCodeAt(0));
        break;

        default:
        break;
    }
}
return str;
}

Answer 5

I think this will work for you:

function makeid() {
  var text = "";
  var possible = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";

  for (var i = 0; i < 5; i++)
    text += possible.charAt(Math.floor(Math.random() * possible.length));

  return text;
}

console.log(makeid());

Answer 6

function randomstring(L) {
  var s = '';
  var randomchar = function() {
    var n = Math.floor(Math.random() * 62);
    if (n < 10) return n; //1-10
    if (n < 36) return String.fromCharCode(n + 55); //A-Z
    return String.fromCharCode(n + 61); //a-z
  }
  while (s.length < L) s += randomchar();
  return s;
}
console.log(randomstring(5));