Narrow a union in TypeScript
TypeScript interview exercise on TypeScript, difficulty 2 of 3. Solve it in the editor beside a worked example; the tests run the moment you do.
Write describe(x: string | number | null): string returning "none" for null, the upper-cased string for strings, and the number formatted with two decimals for numbers.
Each exercise pairs a worked example with a twin problem to solve in a real editor; the tests run the moment you do. Progress is saved in your browser, and in your account if you sign in.