text: function handler(event) {
    // read user input from event
    const input = event.target.value;
  
    // execute core logic
    const reversedUppercase = reverseAndUpper(input);
  
    // render result for user
    document.getElementById('output').innerHTML = reversedUppercase;
  
    // log action for developers
    console.log('\n--- user action ---');
    console.log('input:', typeof input + ',', input);
    console.log('reversedUppercase:', typeof reversedUppercase + ',', reversedUppercase);
  }
  