Counter with closure in TypeScript
TypeScript interview exercise on Functions, 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 makeCounter(start = 0) that returns an object with inc(), dec(), and value() methods sharing private state. inc and dec return the new value.
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.