JavaScript TypeScript Basics 4

Question 1

What is a discriminated union in TypeScript?

Accepted Answer

A union where each member has a common literal property used to narrow the type

Answer

Discriminated unions use a shared literal property (discriminant) to narrow which union member is in use inside conditional blocks.

Question 2

What does enabling `strict` mode in `tsconfig.json` do?

Accepted Answer

Enables a set of strict type-checking options including `strictNullChecks`, `noImplicitAny`, and others

Answer

The `strict` flag is a shorthand that enables a broad set of type safety options simultaneously.

Question 3

What is the output of TypeScript compilation?

Accepted Answer

JavaScript files

Answer

TypeScript compiles down to plain JavaScript files that can run in any JavaScript environment.

Question 4

Which of the following correctly uses an intersection type in TypeScript?

Accepted Answer

type AB = A & B;

Answer

The `&` operator creates an intersection type, combining all properties of both types into one.

Question 5

What does the `?. ` (optional chaining) operator do in TypeScript?

Accepted Answer

Safely accesses a property, returning undefined instead of throwing if the object is null or undefined

Answer

Optional chaining (`?.`) short-circuits to `undefined` if the left-hand side is null or undefined, preventing runtime errors.

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