A random string generator, useful for passwords and the like. Created in Node.js, but as far as I can tell with work in browsers as well

randomString.js

/**
 * Random String
 *
 * Generates a random string of specified length using charSet.
 *
 * Optional charSet can either be a RegExp MATCH or String of allowed characters
 * if not provided then (nearly) all characters on a UK Keyboard will be used.
 *
 * @param {Int} len Length of random string
 * @param {String|RegExp} charSet The character set to use
 * @returns {string}
 */
function randomString(len, charSet) {
  var randomString = ""; // Initialise
  var allChars = "abcdefghijklmnopqrstuvwxyz" + // Lowercase
      "ABCDEFGHIJKLMNOPQURSTUVXYZ" + // Uppercase
      "0123456789" + // Numeric
      ",.?!'\"(){}[]<>£$€@#%^&\\/*-+=_~`¬| "; // Other Characters

  // charSet is optional, default to every character
  if (typeof charSet === "undefined") {
    charSet = allChars;
  }
  // If charSet is regex match from allChars
  if (charSet instanceof RegExp) {
    charSet = allChars.match(charSet);
  }

  // Create string of provided length with random characters from charSet
  for (var i=0; i < len; i++) {
    randomString += charSet[Math.floor((Math.random() * charSet.length))];
  }

  // Return the generated string
  return randomString;
};