Events: on tap, do this — App development for students

Developer's tip

When this, do that — “every event (a tap, a timer, typing) runs its handler code”

1. Event → handler → action: “on tap, do this”.
2. The handler runs once for every tap.
3. Counter: start + taps × step. A limit stops it growing; on = !on flips ON / OFF.

Use it for: Making buttons do something: counters, like buttons, switches and greetings.

Worked example: 👆 The user taps the button 5 times. What number does the label show now?
let stars = 3;
button.onTap = function () {
  stars = stars + 2;
  label.text = stars;
}; → 13

✏️ Practice

Work it out in your head or on paper, type the answer and press Check. Stuck? Press “Show me how”.

🏁 Lesson 17 test

20 questions. Check each answer, then go to the next one. Get 16 or more right to pass.

🏅 Sign in with Google to earn the 👆 Event Handler Hero badge when you pass — and a certificate when you finish all 8 lessons of Part 3 · Logic and Building. You can still take the test without signing in.

🖨️ App Dev Worksheet: Events

• Worksheet set 1 (PDF)
• Worksheet set 2 (PDF)
• Worksheet set 3 (PDF)