Workshop › Conway's Game of Life › Step 20 of 32

Space to play, N to step

What we are doing

The keys now just name a button: a small table turns Space into 'Play' and N into 'Step', and press does the rest.

```js
document.addEventListener('keydown', (event) => {
  const keys = { ' ': 'Play', n: 'Step' }
  const button = keys[event.key.toLowerCase()]
  if (!button) return
  event.preventDefault()
  press(button)
})
```

What it means

• { ' ': 'Play', n: 'Step' } is an object used as a table: keys['n'] is 'Step', keys[' '] (Space) is 'Play'. A key that is not in it gives undefined.
• if (!button) return stops for keys we do not use.
• event.preventDefault() stops the browser's own action, like Space scrolling the page.

Your turn

Inside the keydown listener, replace the if (... === 'n') step() line with the five new lines.

Skills: Keyboard and mouse input

← One place for the buttons Clear and shuffle →

All steps

1. The board
2. Measure the grid
3. One living cell
4. A function that draws
5. The world in memory
6. Draw every living cell
7. A random soup
8. Count the neighbours
9. Four rules
10. Draw again and again
11. Next generation with N
12. Count the generations
13. Show the generation
14. A world without edges
15. Count the living
16. A generation every few frames
17. Let it live
18. Running or not
19. One place for the buttons
20. Space to play, N to step
21. Clear and shuffle
22. Where is the pointer?
23. Which cell?
24. Click a cell
25. Paint or erase?
26. Drag to paint
27. Patterns from text
28. The glider gun
29. Fire the gun
30. Buttons on the screen
31. Tap the buttons
32. Build it yourself: a world at rest