NonNullable type in Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the NonNullable<T> type do in TypeScript?

It creates a new type by removing null and undefined from the type T. This means the resulting type cannot be null or undefined.

beginner

How would you use NonNullable to exclude null and undefined from a type string | null | undefined?

You write NonNullable<string | null | undefined>, which results in just string.

beginner

True or False: NonNullable<number | null | undefined> is the same as number.

True. NonNullable removes null and undefined, leaving only number.

intermediate

Why is NonNullable useful in TypeScript?

It helps prevent errors by ensuring variables do not hold null or undefined values, which can cause runtime problems.

beginner

What happens if you apply NonNullable to a type that does not include null or undefined?

The type stays the same because there is nothing to remove.

What does NonNullable<string | null | undefined> evaluate to?

A string

B string | null

C null | undefined

D string | undefined

NonNullable removes null and undefined, leaving only string.

Which values are removed by NonNullable<T>?

A null and false

B false and 0

C undefined and 0

D null and undefined

NonNullable specifically removes null and undefined from the type.

If a variable is typed as NonNullable<number | null>, what values can it hold?

A Numbers and null

B Only numbers

C Only null

D Numbers and undefined

The NonNullable type removes null, so only numbers remain.

What is the main benefit of using NonNullable in your code?

A To avoid runtime errors from null or undefined values

B To allow more null values

C To convert types to strings

D To add undefined to types

NonNullable helps catch errors early by disallowing null and undefined.

What happens if you apply NonNullable to a type like boolean?

A It becomes undefined

B It becomes never

C The type stays as boolean

D It becomes null

Since boolean does not include null or undefined, it remains unchanged.

Explain what the NonNullable type does and give an example.

Think about how it cleans a type from empty values.

Why is it helpful to use NonNullable in TypeScript code?

Consider what problems null or undefined can cause.