Establishing a Secure Password Generator for Your User Base

password-generator.js

// Valid characters.
var characters =
  "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ" +
  "0123456789`~!@#$%^&*()_-+=[{]}|;:,.<>/?";

// password(X) will return a password of length X.
// password() will return a password of length 12.
var password = function(size) {

  // Placeholder string, where our final password will end up.
  var temp = "";
  
  // If size is set, use it.
  // If size is not set (or 0), default to a length of 12.
  var len = size || 12; 

  // We will choose a random character this many times.
  for (var x = 0; x < len; x++) {

    // Generate a random number from 0 to 1 (think percentage).
    var randomNumber = Math.random();

    // Multiply by the number of characters in our list.
    // The total length times a percentage will give us
    // an exact location in our string of characters.
    //   0% of 10 characters will be the  1st character.
    //  50% of 10 characters will be the  5th character.
    // 100% of 10 characters will be the 10th character.
    var randomFloatingIndex = randomNumber * characters.length;

    // Round this index down because indices are whole numbers that start at 0.
    var randomIndex = Math.floor(randomFloatingIndex);

    // Get the character at this random index.
    var randomCharacter = characters.charAt(randomIndex);

    // Append that character to our password-in-the-making.
    temp += randomCharacter;
  }

  // Return our password-in-the-making now it is complete.
  return temp;
};