Add Keyboard Input

document.addEventListener('keydown', (event) => {
  const key = event.key;

  if (/^[0-9]$/.test(key)) {
    handleAction('digit', key);
    return;
  }

  if (key === '.') {
    handleAction('decimal');
    return;
  }

  const operations = {
    '+': '+',
    '-': '-',
    '*': '*',
    '/': '/'
  };

  if (operations[key]) {
    handleAction('operation', operations[key]);
    return;
  }

  if (key === 'Enter' || key === '=') {
    event.preventDefault();
    handleAction('equals');
    return;
  }

  if (key === 'Backspace') {
    handleAction('backspace');
    return;
  }

  if (key === 'Escape') {
    handleAction('clear');
  }
});