Is it possible for a Typescript class to struggle with implementing a basic interface that includes a

Question

Is it possible for a Typescript class to struggle with implementing a basic interface that includes a

I can't seem to figure out what's wrong with this code. I made a simple test class that follows an interface with a constructor, but the Typescript compiler is flagging an issue.

Here's BaseEntity.ts:

export interface IBaseEntity {
  id: string
  new(_id?: string, _data?: any)
}

This is Test.ts:

class Test implements IBaseEntity {
  id: string
  constructor(_id?: string, _data?: any) {
    this.id = 'MOCK_ID'
  }
}

The error message states:

Class 'Test' incorrectly implements interface 'IBaseEntity'.
  Type 'Test' does not match the signature 'new (_id?: string | undefined, _data?: any): any'.

If anyone could quickly point me in the right direction, that would be greatly appreciated. It seems correct to me, but maybe I'm missing something. Thanks in advance!

typescript

Answer 1

Answer №1

A common misconception exists regarding the purpose of the implements keyword. It actually ensures that the instance type of a class meets the requirements set by the interface. Remember, the constructor belongs to the class type, not the instance type.

To differentiate between the static and instance parts of an interface:

export interface IBaseEntity {
  id: string
}

export interface IBaseEntityClass {
    new(_id?: string, _data?: any): IBaseEntity
}

class Test implements IBaseEntity {
  id: string
  constructor(_id?: string, _data?: any) {
    this.id = 'MOCK_ID'
  }
}

let baseEntityClass: IBaseEntityClass = Test; // Test fulfills the contract of IBaseEntityClass

new baseEntityClass("", {}) // constructing through IBaseEntityClass interface

Playground Link

Although it's not currently possible to specify that a class type must implement a specific interface, errors would arise if Test lacked the required constructor during the assignment

let baseEntityClass: IBaseEntityClass = Test

.

Answer 2

A common misconception exists regarding the purpose of the implements keyword. It actually ensures that the instance type of a class meets the requirements set by the interface. Remember, the constructor belongs to the class type, not the instance type.

To differentiate between the static and instance parts of an interface:

export interface IBaseEntity {
  id: string
}

export interface IBaseEntityClass {
    new(_id?: string, _data?: any): IBaseEntity
}

class Test implements IBaseEntity {
  id: string
  constructor(_id?: string, _data?: any) {
    this.id = 'MOCK_ID'
  }
}

let baseEntityClass: IBaseEntityClass = Test; // Test fulfills the contract of IBaseEntityClass

new baseEntityClass("", {}) // constructing through IBaseEntityClass interface

Playground Link

Although it's not currently possible to specify that a class type must implement a specific interface, errors would arise if Test lacked the required constructor during the assignment

let baseEntityClass: IBaseEntityClass = Test

.

Is it possible for a Typescript class to struggle with implementing a basic interface that includes a

Answer №1

Similar questions

Incorporate Select2 functionality within the Angular2 application

A guide on setting up a countdown timer in Angular 4 for a daily recurring event with the help of Rxjs Observable and the Async Pipe

Enhancing Mongoose promises with Bluebird in a TypeScript environment

Displaying continuous hours on the X-Axis within a 24-hour time series using Recharts

What methods can I use to implement phone number validation in Ionic 2?

Displaying an error message following the dynamic retrieval of the input field's value

Alphabetically sorting objects in an array using Angular

A guide on incorporating Union Types in TypeScript

Unveiling RxJs: The secret to extracting the notifier value using the takeuntil operator

Utilizing React Typescript to dynamically render a duo of components

Using TypeScript and encountering Error TS2345 when trying to utilize Promise.all() in a dialog component

TS: How can we determine the type of the returned object based on the argument property?

Invalid Argument: Cannot use an empty value with the AsyncPipe at invalidArgumentError

Navigating through code in a monorepo using VSCode, Lerna, and Typescript

The occurrence of a loading error arises when attempting to load the second component, displaying the message 'The template instructed for component SidebarComponent is

Simulating service calls in Jest Tests for StencilJs

What could be causing my vis.js network's node hover popups to not function properly?

Is there a way to limit a TypeScript function to only accept `keyof` values corresponding to fields of a specific type?

"Error: Retrieving the body data from the Express request

Are the missing attributes the type of properties that are absent?