Exclude type in Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the Exclude<T, U> type do in TypeScript?

It creates a new type by removing from T all types that are assignable to U. Think of it as filtering out unwanted types from a set.

beginner

Given type A = 'a' | 'b' | 'c' and type B = 'a' | 'c', what is Exclude<A, B>?

The result is 'b' because 'a' and 'c' are removed from A since they are in B.

intermediate

How can Exclude help when working with union types?

It helps you create a new type by excluding certain members from a union, making your types more precise and avoiding unwanted values.

beginner

Is Exclude<string | number, number> equivalent to string?

Yes. It removes number from the union, leaving only string.

intermediate

Can Exclude be used with non-union types?

Yes, but if T is not a union, it either returns T if it is not assignable to U, or never if it is assignable.

What is the result of Exclude<'x' | 'y' | 'z', 'y' | 'a'>?

A 'x' | 'z'

B 'y' | 'a'

C 'x' | 'y' | 'z'

D 'a'

The type removes 'y' from the first union. Since 'a' is not in the first union, only 'y' is removed, leaving 'x' and 'z'.

Which utility type removes types from a union?

A Pick

B Partial

C Exclude

D Record

Exclude removes types from a union. The others serve different purposes.

What does Exclude<number | string, string> evaluate to?

A number

B string

C number | string

D never

It removes string from the union, leaving only number.

If T is 'a' and U is 'a', what is Exclude<T, U>?

A unknown

B 'a'

C string

D never

Since T is assignable to U, it is excluded, resulting in never.

Can Exclude be used to exclude types other than string literals?

A No, only string literals

B Yes, it works with any types

C Only with numbers

D Only with boolean

Exclude works with any types, including primitives, objects, and unions.

Explain how the Exclude type works in TypeScript and give a simple example.

Think about filtering out unwanted types from a set.

Describe a practical scenario where using Exclude would help improve your TypeScript code.

Consider when you want to remove some options from a list of possible values.