Question 1

How does contextual typing work?

Accepted Answer

TS infers types from location — e.g. callback args from parameter types of a function. Lets you omit annotations safely. Breaks when context is lost (extracted functions).

Question 2

When should you annotate vs rely on inference?

Accepted Answer

Annotate exported APIs and boundaries; infer locals when obvious. Explicit return types document contracts and catch impl drift.

Question 3

Why does let x = [] become any[]?

Accepted Answer

Insufficient elements to infer; widens unsafely without context. Annotate as string[] or use as const / satisfies. noImplicitAny helps catch.

Question 4

as const assertion effects?

Accepted Answer

Narrows to literal types and makes tuples/readonly deeply for literals. Unlocks discriminated unions and template literal precision.

Question 5

Return type inference with complex conditionals?

Accepted Answer

May widen or become hard to read — annotate exports. Hover to verify. Split functions to guide inference.

Question 6

Inference across generic call chains?

Accepted Answer

Each step should propagate type args; broken if intermediate typed as any/unknown poorly. Helper identity functions and careful generics preserve types.

Question 7

Design APIs for good inference.

Accepted Answer

Prefer arguments that carry literals, overloads ordered well, avoid early widening. Test inference with type-level unit tests.

Type Inference TypeScript Interview Questions

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