Javascript (node.js) Specific Random String Builder

Question

I'm looking for an efficient way to build a random string that has specific requirements but can vary in length. It must:

Contain at least one uppercase character.
Contain at least one lowercase character.
Contain at least one number.
Contain at least one of the special characters: _-|@.,?/!~#$%^&*(){}[]+=

The random string doesn't have to be unique but if it is, its better. It will be used in a node.js server so any crypto library can be made use of. I saw Math.random().toString(36) which comes close but doesn't get me everything. I'm not sure if I should just try to build a regex for this.

A regex would be used to validate your string/requirements. It would not generate a string. — Buh Buh, Jun 13 '13 at 13:55

maerics · Accepted Answer · 2013-06-13T16:38:17.207

var randomString = (function() {
  // Define character classes to pick from randomly.
  var uppers = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
  var lowers = 'abcdefghijklmnopqrstuvwxyz';
  var numbers = '0123456789';
  var specials = '_-|@.,?/!~#$%^&*(){}[]+=';
  var charClasses = [uppers, lowers, numbers, specials];
  var minLen = charClasses.length;
  function chooseRandom(x) {
    var i = Math.floor(Math.random() * x.length);
    return (typeof(x)==='string') ? x.substr(i,1) : x[i];
  }
  // Define the function to actually generate a random string.
  return function(maxLen) {
    maxLen = (maxLen || 36);
    if (maxLen < minLen) { throw new Error('length must be >= ' + minLen); }
    do { // Append a random char from a random char class.
      var str='', usedClasses={}, charClass;
      while (str.length < maxLen) {
        charClass = chooseRandom(charClasses);
        usedClasses[charClass] = true;
        str += chooseRandom(charClass);
      }
      // Ensure we have picked from every char class.
    } while (Object.keys(usedClasses).length !== charClasses.length);
    return str;
  }
})();

randomString(); // => "o4m3H@YC7j0r@^gsY@1vlg2]cI66|9^beZ1)"
randomString(); // => "R6-K0Kq%4O0Je*=iPbVaV|bo-_,,g[j8wTW2"
randomString(); // => "!uu5NUWs1P}SRN78l}32Gno$]2m5PV+h+wTG"

Is that forEach loop needed? It seems to just limit the first couple of characters to a certain order (1st is uppers, second is lowers, etc) — Xerri, Jun 13 '13 at 15:41
@thearchitect: I added your idea of extracting the "minLen" constant. — maerics, Jun 13 '13 at 16:38

Casimir et Hippolyte · Answer 2 · 2013-06-13T14:01:17.430

0

Regex are used to check, capture, split or replace something in a string, you can't build something from zero with them.

However you can make some replacement in a string that contain a random generated number to have that you want.

edited Jun 13 '13 at 14:01

answered Jun 13 '13 at 13:55

Casimir et Hippolyte

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I thought of that but it will loose a level of uniqueness if I'm just replacing chars. ATM I'm trying Math.random() to build the string. – Xerri Jun 13 '13 at 14:03

Javascript (node.js) Specific Random String Builder

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