Workshop › OutRun-style Racer › Step 13 of 44

Which keys are down?

What we are doing

The arrow keys will be the pedals. We keep the keys that are held down in an object, keys: true while a key is down, false after it is released. Then update can ask every frame whether up is held.

```js
const keys = {}

document.addEventListener('keydown', (event) => {
  keys[event.key] = true
  if (event.key.startsWith('Arrow')) event.preventDefault()
})
document.addEventListener('keyup', (event) => {
  keys[event.key] = false
})
```

What it means

addEventListener('keydown', ...) runs the function whenever a key is pressed; event.key is its name, like 'ArrowUp'.
keys[event.key] = true writes into the field with that name; keyup writes false.
preventDefault() stops the arrow keys from scrolling the page.

Your turn

Under let speed write const keys = {}.
Above function update() { write the two listeners, followed by an empty line.

Skills: Keyboard and mouse input

← Moving is one number The gas pedal →

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