script.js

let insert = document.querySelector(".insert__value");
let result = document.querySelector(".result__value");
let buttons = document.querySelectorAll(".data");
let cancel = document.querySelector(".cancel");
let clear = document.querySelector(".clear");
let negative = document.querySelector(".negative");
let equal = document.querySelector(".equal");


buttons.forEach(button => {
  button.addEventListener('click', function(e) {
    let value = e.target.dataset.num;
    let qtdNumbers = insert.value;

    if (qtdNumbers.length < 25) {
      insert.value += value;
    }
  })
});

cancel.addEventListener('click', () => {
  let lastNumber = insert.value.slice(0, insert.value.length - 1);
  insert.value = lastNumber;
});

clear.addEventListener('click', () => {
  insert.value = "";
  result.value = "";
});

equal.addEventListener('click', () => {
  if(insert.value === '') {
      result.value = "";
  }
  else {
      let answer = eval(insert.value);
      result.value = answer;
  }
});

negative.addEventListener('click', () => {
  if (Math.sign(insert.value) === 1) {
    let insertNegative = `-${insert.value}`
    insert.value = insertNegative;
  }
  else {
    let insertPositive = insert.value.replace('-', '');
    insert.value = insertPositive;
  }
});