script.js

const resultEl = document.getElementById('result')
const lengthEl = document.getElementById('length')
const uppercaseEl = document.getElementById('uppercase')
const lowercaseEl = document.getElementById('lowercase')
const numbersEl = document.getElementById('numbers')
const symbolsEl = document.getElementById('symbols')
const generateEl = document.getElementById('generate')
const clipboardEl = document.getElementById('clipboard')

const randomFunc = {
  lower: getRandomLower,
  upper: getRandomUpper,
  number: getRandomNumber,
  symbol: getRandomSymbol
}

generateEl.addEventListener('click', () => {
  const length = +lengthEl.value
  const hasLower = lowercaseEl.checked
  const hasUpper = uppercaseEl.checked
  const hasNumber = numbersEl.checked
  const hasSymbol = symbolsEl.checked

  resultEl.innerText = generatePassword(hasLower,hasUpper,hasNumber,hasSymbol, length);
})

function generatePassword(lower,upper,number, symbol,length) {
  let generatedPassword = ''
  const typesCount = lower + upper + number + symbol
  const typesArr = [{lower}, {upper}, {number}, {symbol}].filter(item => Object.values(item)[0])
  
  if(typesCount === 0) {
    return ''
  }

    for(let i = 0; i < length; i += typesCount ) {
      typesArr.forEach(type => {
        const funcName = Object.keys(type)[0]
        generatedPassword += randomFunc[funcName]()
      })
    }
    const finalPassword = generatedPassword.slice(0, length)
    return finalPassword
  }


function getRandomLower() {
  return String.fromCharCode(Math.floor(Math.random() * 26) + 97)
}

function getRandomUpper() {
  return String.fromCharCode(Math.floor(Math.random() * 26) + 67)
}

function getRandomNumber() {
  return String.fromCharCode(Math.floor(Math.random() * 10) + 48)
}

function getRandomSymbol() {
 const symbols = '!@#$%^&*(){}[]=/,.+-'
 return symbols[Math.floor(Math.random() * symbols.length)]
}