JavaScript Password Generator Sometimes Not Including Character Selections?

Hello Stack Overflow!

This is my first time posting on the site so please bare with me and my question. My class was tasked with individually creating a password generator using JavaScript. Thankfully I had gotten most of the application operating correctly, but I've gotten stuck on a problem.

Example: The user chooses to have 8 characters in their password and chooses to include special, lowercase, and uppercase characters. When the password is generated sometimes it won't include all of the character selections. (Sometimes it'll generate a password with both special and uppercase characters, but not have a single lowercase character).

I've been finished with this assignment for a minute now, but my goal is to understand what I can do to fix this problem and complete this app anyway. I was thinking of potentially removing the passwordOptions object and turning each option into an array of their own, what are your thoughts?

Thank you so much for any suggestions! :D

// passwordOptions contains all necessary string data needed to generate the password
const passwordOptions = {
  num: "1234567890",
  specialChar: "!@#$%&'()*+,^-./:;<=>?[]_`{~}|",
  lowerCase: "abcdefghijklmnopqrstuvwxyz",
  upperCase: "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
};

document.getElementById('generate').addEventListener('click', function() {
  alert(generatePassword());
});

// Executes when button is clicked
let generatePassword = function() {

  // initial state for password information
  let passInfo = "";

  // ask user for the length of their password
  let characterAmount = window.prompt("Enter the amount of characters you want for your password. NOTE: Must be between 8-128 characters");

  // If the character length doesn't match requirements, alert the user
  if (characterAmount >= 8 && characterAmount < 129) {

    // ask if user wants to include integers
    let getInteger = window.confirm("Would you like to include NUMBERS?");

    // if user wants to include numbers
    if (getInteger) {
      // add numerical characters to password data 
      passInfo = passInfo + passwordOptions.num;
    };

    // ask if user wants to include special characters
    let getSpecialCharacters = window.confirm("Would you like to include SPECIAL characters?");

    // if user wants to include special characters 
    if (getSpecialCharacters) {
      // add special characters to password data
      passInfo = passInfo + passwordOptions.specialChar;
    };

    // ask if user wants to include lowercase characters
    let getLowerCase = window.confirm("Would you like to include LOWERCASE characters?");

    // if user wants to include lowercase characters
    if (getLowerCase) {
      // add lowercase characters to password data
      passInfo = passInfo + passwordOptions.lowerCase;
    };

    // ask if user wants to include uppercase characters
    let getUpperCase = window.confirm("Would you like to include UPPERCASE characters?");

    // if user wants to include uppercase characters
    if (getUpperCase) {
      // add uppercase characters to password data 
      passInfo = passInfo + passwordOptions.upperCase;
    };

    // ensure user chooses at least one option
    if (getInteger !=true && getSpecialCharacters !=true && getLowerCase !=true && getUpperCase !=true) {
      // notify user needs to select at least one option
      window.alert("You need to select at least one option, please try again!");
      // return user back to their questions
      return generatePassword();
    };

    // randomPassword is an empty string that the for loop will pass information in
    let randomPassword = "";

    // for loop grabs characterAmount to use
    for (let i = 0; i < characterAmount; i++) {
      //passInfo connects to charAt that uses both Math.floor and random to take the length of passInfo and randomize the results
      randomPassword += passInfo[Math.floor(Math.random() * passInfo.length)];
    };

    // return password results
    return randomPassword;
  }
  // if user's response is invalid
  else {
    // alert user
    window.alert("You need to provide a valid length!");
    // return user back to their questions
    
    /* Removed for testing purposes to break the endless loop. */
    // return generatePassword();
  }
};

<button id="generate">Run</button>

Solution

The best way I can imagine is to pick one character from each selected category, then select the remaining characters randomly, finally, shuffle the selected characters.

You can do it like this:

// passwordOptions contains all necessary string data needed to generate the password
const passwordOptions = {
  num: "1234567890",
  specialChar: "!@#$%&'()*+,^-./:;<=>?[]_`{~}|",
  lowerCase: "abcdefghijklmnopqrstuvwxyz",
  upperCase: "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
};

document.getElementById('generate').addEventListener('click', function() {
  alert(generatePassword());
});

// Executes when button is clicked
let generatePassword = function() {

  // initial state for password information
  let passInfo = "";
  
  // list of chosen characters
  const passChars = [];

  // ask user for the length of their password
  let characterAmount = window.prompt("Enter the amount of characters you want for your password. NOTE: Must be between 8-128 characters");

  // If the character length doesn't match requirements, alert the user
  if (characterAmount >= 8 && characterAmount <= 128) {

    // ask if user wants to include integers
    const getInteger = window.confirm("Would you like to include NUMBERS?");

    // if user wants to include numbers
    if (getInteger) {
      // add numerical characters to password data 
      passInfo += passwordOptions.num;
      // add a number to the list of chosen characters
      passChars.push(getRandomChar(passwordOptions.num));
    };

    // ask if user wants to include special characters
    const getSpecialCharacters = window.confirm("Would you like to include SPECIAL characters?");

    // if user wants to include special characters 
    if (getSpecialCharacters) {
      // add special characters to password data 
      passInfo += passwordOptions.specialChar;
      // add a special character to the list of chosen characters
      passChars.push(getRandomChar(passwordOptions.specialChar));
    };

    // ask if user wants to include lowercase characters
    const getLowerCase = window.confirm("Would you like to include LOWERCASE characters?");

    // if user wants to include lowercase characters
    if (getLowerCase) {
      // add lowercase characters to password data 
      passInfo += passwordOptions.lowerCase;
      // add a lowercase character to the list of chosen characters
      passChars.push(getRandomChar(passwordOptions.lowerCase));
    };

    // ask if user wants to include uppercase characters
    const getUpperCase = window.confirm("Would you like to include UPPERCASE characters?");

    // if user wants to include uppercase characters
    if (getUpperCase) {
      // add uppercase characters to password data 
      passInfo += passwordOptions.upperCase;
      // add an uppercase character to the list of chosen characters
      passChars.push(getRandomChar(passwordOptions.upperCase));
    };

    // ensure user chooses at least one option -- passInfo will be empty if they don't
    if (!passInfo) {
      // notify user needs to select at least one option
      window.alert("You need to select at least one option, please try again!");
      // return user back to their questions
      return generatePassword();
    };

    // while there aren't enough characters
    while(passChars.length < characterAmount) {
      // choose a random char from charInfo
      passChars.push(getRandomChar(passInfo));
    };

    // shuffle the list of characters using Fisher-Yates algorithm
    // see https://stackoverflow.com/a/2450976/8376184
    for(let i = passChars.length - 1; i > 0; i--){
      const swapIndex = Math.floor(Math.random() * (i + 1));
      const temp = passChars[i];
      passChars[i] = passChars[swapIndex];
      passChars[swapIndex] = temp;
    };

    // return the password character list concatenated to a string
    return passChars.join("");
  }
  // if user's response is invalid
  else {
    // alert user
    window.alert("You need to provide a valid length!");
    // return user back to their questions
    
    /* Removed for testing purposes to break the endless loop. */
    // return generatePassword();
  }
};

function getRandomChar(fromString){
  return fromString[Math.floor(Math.random() * fromString.length)];
}

<button id="generate">Run</button>

But, as password generators should be cryptographically random, you should use crypto.getRandomValues() instead of Math.random(). You can use this algorithm to convert it to a range of values:

// Generate a random integer r with equal chance in  0 <= r < max.
function randRange(max) {
    const requestBytes = Math.ceil(Math.log2(max) / 8);
    if (!requestBytes) { // No randomness required
        return 0;
    };
    const maxNum = Math.pow(256, requestBytes);
    const ar = new Uint8Array(requestBytes);

    while (true) {
        window.crypto.getRandomValues(ar);

        let val = 0;
        for (let i = 0; i < requestBytes;i++) {
            val = (val << 8) + ar[i];
        };

        if (val < maxNum - maxNum % max) {
            return val % max;
        };
    };
};

You can combine this with the code above like this:

// passwordOptions contains all necessary string data needed to generate the password
const passwordOptions = {
  num: "1234567890",
  specialChar: "!@#$%&'()*+,^-./:;<=>?[]_`{~}|",
  lowerCase: "abcdefghijklmnopqrstuvwxyz",
  upperCase: "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
};

document.getElementById('generate').addEventListener('click', function() {
  alert(generatePassword());
});

// Executes when button is clicked
let generatePassword = function() {

  // initial state for password information
  let passInfo = "";
  
  // list of chosen characters
  const passChars = [];

  // ask user for the length of their password
  let characterAmount = window.prompt("Enter the amount of characters you want for your password. NOTE: Must be between 8-128 characters");

  // If the character length doesn't match requirements, alert the user
  if (characterAmount >= 8 && characterAmount <= 128) {

    // ask if user wants to include integers
    const getInteger = window.confirm("Would you like to include NUMBERS?");

    // if user wants to include numbers
    if (getInteger) {
      // add numerical characters to password data 
      passInfo += passwordOptions.num;
      // add a number to the list of chosen characters
      passChars.push(getRandomChar(passwordOptions.num));
    };

    // ask if user wants to include special characters
    const getSpecialCharacters = window.confirm("Would you like to include SPECIAL characters?");

    // if user wants to include special characters 
    if (getSpecialCharacters) {
      // add special characters to password data 
      passInfo += passwordOptions.specialChar;
      // add a special character to the list of chosen characters
      passChars.push(getRandomChar(passwordOptions.specialChar));
    };

    // ask if user wants to include lowercase characters
    const getLowerCase = window.confirm("Would you like to include LOWERCASE characters?");

    // if user wants to include lowercase characters
    if (getLowerCase) {
      // add lowercase characters to password data 
      passInfo += passwordOptions.lowerCase;
      // add a lowercase character to the list of chosen characters
      passChars.push(getRandomChar(passwordOptions.lowerCase));
    };

    // ask if user wants to include uppercase characters
    const getUpperCase = window.confirm("Would you like to include UPPERCASE characters?");

    // if user wants to include uppercase characters
    if (getUpperCase) {
      // add uppercase characters to password data 
      passInfo += passwordOptions.upperCase;
      // add an uppercase character to the list of chosen characters
      passChars.push(getRandomChar(passwordOptions.upperCase));
    };

    // ensure user chooses at least one option -- passInfo will be empty if they don't
    if (!passInfo) {
      // notify user needs to select at least one option
      window.alert("You need to select at least one option, please try again!");
      // return user back to their questions
      return generatePassword();
    };

    // while there aren't enough characters
    while(passChars.length < characterAmount) {
      // choose a random char from charInfo
      passChars.push(getRandomChar(passInfo));
    };

    // shuffle the list of characters using Fisher-Yates algorithm
    // see https://stackoverflow.com/a/2450976/8376184
    for(let i = passChars.length - 1; i > 0; i--){
      const swapIndex = randRange(i + 1);
      const temp = passChars[i];
      passChars[i] = passChars[swapIndex];
      passChars[swapIndex] = temp;
    };

    // return the password character list concatenated to a string
    return passChars.join("");
  }
  // if user's response is invalid
  else {
    // alert user
    window.alert("You need to provide a valid length!");
    // return user back to their questions
    
    /* Removed for testing purposes to break the endless loop. */
    // return generatePassword();
  }
};

function getRandomChar(fromString){
  return fromString[randRange(fromString.length)];
};

// Generate a random integer r with equal chance in  0 <= r < max.
function randRange(max) {
    const requestBytes = Math.ceil(Math.log2(max) / 8);
    if (!requestBytes) { // No randomness required
        return 0;
    };
    const maxNum = Math.pow(256, requestBytes);
    const ar = new Uint8Array(requestBytes);

    while (true) {
        window.crypto.getRandomValues(ar);

        let val = 0;
        for (let i = 0; i < requestBytes;i++) {
            val = (val << 8) + ar[i];
        };

        if (val < maxNum - maxNum % max) {
            return val % max;
        };
    };
};

<button id="generate">Run</button>