Updating a signal immutably in Angular
Angular interview exercise on Signals, difficulty 2 of 3. Solve it in the editor beside a worked example, or cold in Interview mode with the example hidden; the tests run the moment you do.
Write the class for TodoListComponent: a `todos` signal holding the two todos below, a `remaining` computed with how many are not done, and toggle(id) that flips one todo's `done`. Replace the array and the todo you change; never mutate what the signal holds.
Each exercise pairs a worked example with a twin problem to solve in a real editor; the tests run the moment you do. Interview mode hides the example: solve it from memory, without the hint or the solution, and it counts as solved cold. Progress is saved in your browser, and in your account if you sign in.