main.js

function calculate(inputValue) {
  const expression = /\+|\-|\*|\//;
  const numbers = inputValue.split(expression);

  const numberA = parseInt(numbers[0]);
  const numberB = parseInt(numbers[1]);

  const operation = inputValue.match(expression);

  if (Number.isNaN(numberA) || Number.isNaN(numberB) || operation === null) {
    updateResult('Operation not recognized');
    return;
  }

  const calculator = new Calculator();
  calculator.add(numberA);

  let result;
  switch (operation[0]) {
    case '+':
      result = calculator.add(numberB);
      break;
    case '-':
      result = calculator.subtract(numberB);
      break;
    case '*':
      result = calculator.multiply(numberB);
      break;
    case '/':
      result = calculator.divide(numberB);
      break;
    default:
      break;
    }
    
    updateResult(result);
}

function updateResult(result) {
  const element = document.getElementById('result');

  if (element) {
    element.innerHTML = result;
  }
}