Workshop › Frogger-style Crossing › Step 9 of 22

Hit by a car

What we are doing

If a car covers the frog's square, the frog is hit and a new one starts from the bottom. The frog's box is shrunk a little, so only a real overlap counts.

```js
function newFrog() {
  frog = { x: 5, y: START_ROW }
}

function laneAt(row) {
  return LANES.find((lane) => lane.row === row)
}

function die() {
  newFrog()
}

function hitByCar(lane) {
  return items(lane).some((x) => frog.x + 0.15 < x + lane.len && frog.x + 0.85 > x)
}

  const lane = laneAt(frog.y)
  if (!lane) return
  if (hitByCar(lane)) die()
```

What it means

laneAt finds the lane in the frog's row, or undefined on the safe rows.
A car from x to x + len overlaps the frog when the car starts before the frog ends and ends after it starts. The frog counts as 0.15 to 0.85 of its square.
die just starts a new frog for now.

Your turn

Under the offset line, write newFrog and laneAt.
Above DIRECTIONS, write die; above update, write hitByCar.
At the end of update, write the three check lines.

Skills: Collision detection

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