Swapping an implementation in Angular
Angular interview exercise on Dependency injection, 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 an abstract Clock with now(): Date, provided in root with a SystemClock implementation that returns new Date(). GreetingComponent injects Clock and renders <p class="greeting"> reading "Good morning" before 12, "Good afternoon" before 18 and "Good evening" after.
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.