window.onload = () => {
  const calculator = document.forms.calculator

  calculator.addEventListener('click', (e) => {
    if (e.target) {
      if (e.target.matches("input.addon")) {
        calculator.display.value += e.target.value;
      } else if (e.target.matches('input#clear')) {
        calculator.display.value = '';
      } else if (e.target.matches('input#solve')) {
        calculator.display.value = eval(calculator.display.value)
      }
    }
  });
}