How do you type and guard a string-or-string-array argument?
Tests union typing and runtime narrowing. Annotate as `string | string[]`, then branch with `Array.isArray()`. Strong answers note `typeof` returns `"object"` for arrays and that assertions bypass safety.
Tests union types and TypeScript narrowing. A strong answer types the parameter as `string | string[]` and branches with `Array.isArray()`, handling arrays first and strings second. Candidates should explain that `typeof` returns `"object"` for arrays, so it cannot distinguish them, and that `Array.isArray()` is the idiomatic runtime check. They should avoid type assertions like `as string[]`, which bypass compiler safety.
Read the original → typescriptlang.org
- #typescript
- #type-guards
- #union-types
- #narrowing
- #arrays
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