Workshop › Conway's Game of Life › Step 4 of 32

A function that draws

What we are doing

The world will change many times a second, and each time the whole picture must be drawn again. We pack the drawing lines into a function named draw, so one word repaints everything.

```js
function draw() {
  ctx.fillStyle = '#0f172a'
  ctx.fillRect(0, 0, canvas.width, canvas.height)
  ctx.fillStyle = '#1e293b'
  ctx.fillRect(0, TOP, COLS * CELL, ROWS * CELL)

  ctx.fillStyle = '#4ade80'
  ctx.fillRect(3 * CELL, TOP + 2 * CELL, CELL - 1, CELL - 1)
}

draw()
```

What it means

• function draw() { ... } defines the recipe; it does not run yet.
• The lines between { and } are its body, indented by two spaces.
• draw() with parentheses runs it. Each run paints the background first, which wipes the old picture.

Your turn

Wrap all the drawing lines in function draw() { ... } (indented by two spaces) and call draw() after it.

Skills: Functions

← One living cell The world in memory →

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