Workshop › Conway's Game of Life › Step 5 of 32

The world in memory

What we are doing

The picture is not the world; the world is data. Each cell is a number, 1 alive and 0 dead, and the grid is a list of rows, each row a list of cells: grid[row][col]. We make an all-dead grid.

```js
let grid // grid[row][col]: 1 alive, 0 dead

const emptyGrid = () => Array.from({ length: ROWS }, () => Array(COLS).fill(0))

function reset() {
  grid = emptyGrid()
}

reset()
draw()
```

What it means

• let grid makes a variable whose value can change later (const cannot). It is empty until reset fills it.
• emptyGrid is a short arrow function: it returns whatever is right of =>.
• Array(COLS).fill(0) is one row of 60 zeros. Array.from({ length: ROWS }, () => ...) calls the little function 48 times and makes a list of the 48 results: a new row each time.
• reset() puts a fresh empty grid in grid; it runs once, before the first draw().

Your turn

1. Under const TOP = 36, after an empty line, write let grid, emptyGrid and reset as shown.
2. At the bottom, write reset() above draw(). Press Run.

Skills: Arrays and objects

← A function that draws Draw every living cell →

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