ConstructorParameters type in Typescript - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to extract constructor parameter types using ConstructorParameters.

Typescript

type Params = [1]<Date>;

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

AReturnType

BParameters

CConstructorParameters

DInstanceType

Attempts:

3 left

💡 Hint

Common Mistakes

Using Parameters instead of ConstructorParameters

Using ReturnType which extracts return types

Using InstanceType which extracts instance types

The ConstructorParameters utility type extracts the parameter types of a class constructor as a tuple.

2fill in blank

medium

Complete the code to define a class and extract its constructor parameter types.

Typescript

class Person {
  constructor(public name: string, public age: number) {}
}
type PersonParams = [1]<typeof Person>;

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

AConstructorParameters

BParameters

CReturnType

DInstanceType

Attempts:

3 left

💡 Hint

Common Mistakes

Using Parameters which works with functions, not constructors

Using InstanceType which gives the instance type, not parameters

ConstructorParameters extracts the parameter types of the Person constructor as a tuple [string, number].

3fill in blank

hard

Fix the error in the code to correctly extract constructor parameters of a class.

Typescript

class Car {
  constructor(make: string, year: number) {}
}
type CarParams = ConstructorParameters<[1]>;

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

Atypeof Car

BCar

CCarConstructor

DInstanceType<Car>

Attempts:

3 left

💡 Hint

Common Mistakes

Using the class name directly instead of typeof

Using InstanceType which is for instances, not constructors

You must use typeof Car to refer to the constructor type of the class Car when using ConstructorParameters.

4fill in blank

hard

Fill both blanks to create a function that accepts constructor parameters of a class.

Typescript

function createInstance(cls: [1], ...args: [2]) {
  return new cls(...args);
}

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

Anew (...args: any) => any

BConstructorParameters<typeof cls>

Dany[]

Attempts:

3 left

💡 Hint

Common Mistakes

Using instance type instead of constructor signature

Not using ConstructorParameters for the args

The first blank requires a constructor type signature. The second blank uses ConstructorParameters to type the rest parameters.

5fill in blank

hard

Fill all three blanks to define a generic function that creates instances using constructor parameters.

Typescript

function makeInstance<T extends [1]>(cls: T, ...args: [2]<T>): InstanceType<T> {
  return new cls(...args);
}

type Params<T> = [3]<T>;

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

Anew (...args: any) => any

BConstructorParameters

DParameters

Attempts:

3 left

💡 Hint

Common Mistakes

Using Parameters instead of ConstructorParameters

Not constraining T to a constructor signature

The generic type T extends a constructor signature. The rest arguments use ConstructorParameters of T. The type alias also uses ConstructorParameters.