index.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 clipboard = 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(hasUpper,hasLower,hasNumber,hasSymbol,length)
});

clipboard.addEventListener('click',()=>{
    const textarea = document.createElement('textarea');
    const password = resultEl.innerText;

    if(!password){
        return;
    }
    textarea.value = password;
    document.body.appendChild(textarea);
    textarea.select();
    document.execCommand('copy');
    textarea.remove();
    alert('Password copied to clipboard')
})

function generatePassword(upper,lower,number,symbol,length){
let generatedPassword = '';
const typesCount =upper+ lower+number+symbol;
const typesArr = [{upper},{lower},{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)+65);
}
function getRandomNumber() {
    return (Math.floor(Math.random()*10));
}
function getRandomSymbol() {
    const symbols = '`~!@#$%^&*()_+{}[]|<>,./?';
    return symbols[Math.floor(Math.random()*symbols.length)];
}