Random string generator in Javascript / nonce generator

random-string.js

/*
  Generate a random string of a given length.
  @params:
    length: *required* - length of string to generate 
    kind:   *optional* - character set or sets to use for string generation  (default: 'aA#')
      Available options
        'a' => for lowercase alphabets [a-z]
        'A' => for uppercase alphabets [A-Z]
        '#' => numbers [0-9]
        '!' => special character as defined
        '*' => all of the above
      
      Default charset is AlphaNumeric - equivalent to 'aA#'

  Typical Usage
    console.log(randomString(10));        // alphanumeric strings. Uses 'aA#'
    console.log(randomString(10, 'a'));   // downcase alpha
    console.log(randomString(10, 'A'));   // downcase alpha
    console.log(randomString(19, '#aA')); // case-insensitive AlphaNumric
    console.log(randomString(24, '#A!')); // numbers && upcase alpha && special characters
    console.log(randomString(100, '*'));  // Everything: case-insensitive AlphaNumric && special characters
*/

var randomString = function(length, kind) {
  var i,
      str = '', 
      opts = kind || 'aA#',
      possibleChars = '';

  if (kind.indexOf('*') > -1) opts = 'aA#!'; // use all possible charsets

  // Collate charset to use
  if (opts.indexOf('#') > -1) possibleChars += '0123456789';
  if (opts.indexOf('a') > -1) possibleChars += 'abcdefghijklmnopqrstuvwxyz';
  if (opts.indexOf('A') > -1) possibleChars += 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
  if (opts.indexOf('!') > -1) possibleChars += '~`!@#$%^&*()_+-={}[]:";\'<>?,./|\\';

  for(i = 0; i < length; i++) {
    str += possibleChars.charAt(Math.floor(Math.random() * possibleChars.length));
  }
  return str;
}