Question 1

What are TypeScript utility types?

Accepted Answer

TypeScript utility types are built-in generic types that transform other types. Common ones include Partial (makes all properties optional), Required (makes all required), Pick (selects specific properties), Omit (removes properties), Record (creates object type), and ReturnType (extracts function return type).

Question 2

What are mapped types in TypeScript?

Accepted Answer

Mapped types create new types by transforming each property of an existing type. They use the syntax { [K in keyof T]: NewType }. For example, you can make all properties readonly, optional, or change their types. Built-in utility types like Partial and Required are implemented as mapped types.

Question 3

What are conditional types in TypeScript?

Accepted Answer

Conditional types select one of two types based on a condition, using the syntax T extends U ? X : Y. They enable type-level if/else logic. Combined with 'infer', they can extract types from complex structures. Examples include Extract, Exclude, and ReturnType utility types.

Question 4

How do template literal types work?

Accepted Answer

Template literal types use backtick syntax to create string types from combinations. For example, type Color = 'red' | 'blue'; type Size = 'sm' | 'lg'; type Combo = `${Size}-${Color}` creates 'sm-red' | 'sm-blue' | 'lg-red' | 'lg-blue'. They enable precise string pattern matching at the type level.

TypeScript Type Playground

Load an Example

Built-in Utility Types

Type Challenges

NexTool on GitHub