Higher-order function types in Typescript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a function type that takes a number and returns a number.

Typescript

type NumberFunc = (x: number) => [1];

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

Aboolean

Bnumber

Cvoid

Dstring

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing a return type different from the input type.

Confusing parameter type with return type.

The function takes a number and returns a number, so the return type is number.

2fill in blank

medium

Complete the code to declare a higher-order function type that takes a function (number to number) and returns a function (number to number).

Typescript

type HigherOrder = (fn: (x: number) => number) => [1];

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

Avoid

Bstring

Cnumber

D(x: number) => number

Attempts:

3 left

💡 Hint

Common Mistakes

Using void as return type instead of a function type.

Confusing return type with parameter type.

The higher-order function returns another function that takes a number and returns a number, so the return type is (x: number) => number.

3fill in blank

hard

Fix the error in the function type declaration to correctly type a function that takes a function and returns void.

Typescript

type Func = (callback: (msg: string) => void) => [1];

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

Avoid

Bstring

Cnumber

D(msg: string) => void

Attempts:

3 left

💡 Hint

Common Mistakes

Using a function type as return type instead of void.

Confusing parameter and return types.

The function takes a callback and returns nothing, so the return type is void.

4fill in blank

hard

Fill both blanks to declare a function type that takes a function returning a boolean and returns a function returning a string.

Typescript

type ComplexFunc = (check: () => [1]) => () => [2];

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

Aboolean

Bstring

Cnumber

Dvoid

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up the return types of the parameter and returned functions.

Using void instead of the correct types.

The parameter function returns a boolean, and the returned function returns a string.

5fill in blank

hard

Fill all three blanks to declare a higher-order function type that takes a function (string to number), returns a function taking a number and returning a boolean.

Typescript

type HOF = (fn: (input: [1]) => [2]) => (arg: [3]) => boolean;

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

Astring

Bnumber

Dboolean

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping input and output types.

Using wrong types for the returned function's argument.

The input function takes a string and returns a number. The returned function takes a number and returns a boolean.