script.js

const calculatorDisplay = document.querySelector('h1');
const inputBtns = document.querySelectorAll('button');
const clearBtn = document.getElementById('clear-btn');

let firstValue = 0;
let operatorValue = '';
let nextValue = false;

function numberValue(number) {
  if (nextValue) {
    calculatorDisplay.textContent = number;
    nextValue = false;
  } else {
    const displayValue = calculatorDisplay.textContent;
    calculatorDisplay.textContent =
      displayValue === '0' ? number : displayValue + number;
  }
}

function addDecimal() {
  if (nextValue) return;
  if (!calculatorDisplay.textContent.includes('.')) {
    calculatorDisplay.textContent = `${calculatorDisplay.textContent}.`;
  }
}

const calculate = {
  '/': (firstNumber, secoundNumber) => firstNumber / secoundNumber,
  '*': (firstNumber, secoundNumber) => firstNumber * secoundNumber,
  '+': (firstNumber, secoundNumber) => firstNumber + secoundNumber,
  '-': (firstNumber, secoundNumber) => firstNumber - secoundNumber,
  '=': (firstNumber, secoundNumber) => secoundNumber,
};

function useOperator(operator) {
  const currentValue = Number(calculatorDisplay.textContent);
  if (operatorValue && nextValue) {
    operatorValue = operator;
    return;
  }
  if (!firstValue) {
    firstValue = currentValue;
  } else {
    //console.log(firstValue, operatorValue, currentValue);
    const calculation = calculate[operatorValue](firstValue, currentValue);
    //console.log('calculation:', calculation);
    calculatorDisplay.textContent = calculation;
    firstValue = calculation;
  }
  nextValue = true;
  operatorValue = operator;
}

inputBtns.forEach((inputBtn) => {
  if (inputBtn.classList.length === 0) {
    inputBtn.addEventListener('click', () => numberValue(inputBtn.value));
  } else if (inputBtn.classList.contains('operator')) {
    inputBtn.addEventListener('click', () => useOperator(inputBtn.value));
  } else if (inputBtn.classList.contains('decimal')) {
    inputBtn.addEventListener('click', () => addDecimal());
  }
});

function clearAll() {
  firstValue = 0;
  operatorValue = '';
  nextValue = false;
  calculatorDisplay.textContent = '0';
}

clearBtn.addEventListener('click', clearAll);