Random string generator for JS, JS (ES6), PHP, and Python.

random_string.php

<?php
function random_string($length, $opt_chars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz") {
  for ($l = strlen($opt_chars) - 1, $s = ""; $length--; ) {
    $s .= substr($opt_chars, rand(0, $l), 1);
  }
  return $s;
}

random_string.py

import random
def random_string(length, opt_chars="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"):
  return ''.join([random.choice(opt_chars) for i in range(length)])

randomString.es6.js

function randomString(length, opt_chars = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz') {
  return [...Array(length)].map(_ => opt_chars[~~(Math.random() * opt_chars.length)]).join('');
}

randomString.js

function randomString(length, opt_chars) {
  opt_chars = opt_chars || '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz';
  for (var l = opt_chars.length, s = ''; length--; ) {
    s += opt_chars.charAt(~~(Math.random() * opt_chars.length));
  }
  return s;
}