Intermediate
A score keeper with typed actions
The score keeper's reducer takes action: any and only handles adding points. Type it properly and finish it.
Write type Action as a discriminated union of { type: "add"; points: number }, { type: "undo" } and { type: "reset" }. Type the state as { score: number; history: number[] } (history holds the points of each add, newest last).
Handle every action in a switch, with a default branch that assigns action to a variable of type never. Undo removes the last add; Reset goes back to 0 with an empty history.
Keep the ids: id="score", buttons id="plus1", id="plus5", id="undo", id="reset".
What Check tests
- +1 then +5 shows 6
- Undo removes the last add (back to 1)
- Undo with an empty history does nothing
- Reset goes back to 0 after more adds
- Actions are a discriminated union
- Uses a switch with a never check and no any
Stuck? One hint at a time
The solution unlocks after your first Check. Try first: that is where the learning happens.
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