Basic mapped type syntax in Typescript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a mapped type that makes all properties optional.

Typescript

type PartialType<T> = { [P in keyof T][1] };

Drag options to blanks, or click blank then click option'

A:

B!

C?

D=

Attempts:

3 left

💡 Hint

Common Mistakes

Using ':' instead of '?' which defines the type but does not make it optional.

Using '!' which is a non-null assertion and not valid here.

The question mark (?) after the property name makes the property optional in a mapped type.

2fill in blank

medium

Complete the code to create a mapped type that makes all properties readonly.

Typescript

type ReadonlyType<T> = { [1] [P in keyof T]: T[P] };

Drag options to blanks, or click blank then click option'

Areadonly

Boptional

Cmutable

Dprivate

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'optional' which is not a TypeScript keyword.

Using 'private' which is an access modifier but not valid in mapped types.

The 'readonly' keyword before the property makes all properties readonly in the mapped type.

3fill in blank

hard

Fix the error in the mapped type that tries to change all properties to string type.

Typescript

type Stringify<T> = { [P in keyof T]: [1] };

Drag options to blanks, or click blank then click option'

Aboolean

BT[P]

Cnumber

Dstring

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'T[P]' which keeps the original type instead of changing it.

Using 'number' or 'boolean' which changes the type but not to string.

To change all property types to string, use 'string' as the type for each property.

4fill in blank

hard

Fill both blanks to create a mapped type that makes all properties optional and readonly.

Typescript

type OptionalReadonly<T> = { [1] [P in keyof T][2]: T[P] };

Drag options to blanks, or click blank then click option'

Areadonly

B?

C!

D:

Attempts:

3 left

💡 Hint

Common Mistakes

Placing '?' before the property name instead of after.

Using '!' which is not valid here.

Use 'readonly' before the property name and '?' after it to make properties readonly and optional.

5fill in blank

hard

Fill all three blanks to create a mapped type that changes all properties to readonly, optional, and of type number.

Typescript

type ReadonlyOptionalNumber<T> = { [1] [P in keyof T][2]: [3] };

Drag options to blanks, or click blank then click option'

Areadonly

B?

Cnumber

Dstring

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'string' instead of 'number' for the property type.

Omitting '?' which makes properties required.

Use 'readonly' before the property name, '?' after it, and set the type to 'number' to achieve the desired mapped type.