Understanding the explanation of the function declaration

Question

Understanding the explanation of the function declaration

declare abstract class CustomBootstrapConsole<X extends AppContext, Y extends Options = DefaultOptions> {
    protected customService: CustomConsoleService;
    protected customContainer: X;
    protected readonly customOptions: Y;
    constructor(options: Y);
    protected applyCustomDecorators(): this;
    initialize(): Promise<X>;
    getCustomService(): CustomConsoleService;
    getCustomOptions(): Y;
    launch(commandArgs?: string[]):     
    Promise<CommandResponse>;
    abstract setup(): Promise<X>;
}

I'm delving into the intricacies of this unique ~~function~~ class definition. It's a core feature of the nestjs-console framework. I find myself grappling with understanding the syntax used in the declaration. What is the significance of

class X<Y extends Z, W extends V = U>

and how could I independently research and comprehend this in the future? Thus far, my search for answers within the Typescript documentation has been unfruitful.

Update: Grateful for the insightful responses received! Much appreciated!

javascript typescript nestjs

Answer 1

Answer №1

The concept you are referring to is known as generics.

class A<B extends C, D extends E = F>

In this code snippet, a class named A is being defined with two generic parameters, B and D. The constraint here is that B must extend interface C, while D must extend interface E. Additionally, if the generic parameter D is not provided, it defaults to interface F.

interface C {
    name: string;
}

interface E {
    something: number;
}

interface F extends E {
    somethingElse: boolean;
}

class A<B extends C, D extends E = F> {
    constructor(b: B, d: D) {

    }
}

interface D extends C {
    surname: string;
}

const a: A<D> = {}; // If no generic parameter is specified, it will default to F. The constructor parameter d must be of type F.

Learn more about TypeScript generics here.

Answer 2

The concept you are referring to is known as generics.

class A<B extends C, D extends E = F>

In this code snippet, a class named A is being defined with two generic parameters, B and D. The constraint here is that B must extend interface C, while D must extend interface E. Additionally, if the generic parameter D is not provided, it defaults to interface F.

interface C {
    name: string;
}

interface E {
    something: number;
}

interface F extends E {
    somethingElse: boolean;
}

class A<B extends C, D extends E = F> {
    constructor(b: B, d: D) {

    }
}

interface D extends C {
    surname: string;
}

const a: A<D> = {}; // If no generic parameter is specified, it will default to F. The constructor parameter d must be of type F.

Learn more about TypeScript generics here.

Answer 3

Answer №2

Breaking it down into its individual components.

class Foo<T>

This indicates that Foo is a class that accepts a generic type parameter T, nothing too complex here. When you instantiate Foo, you must specify a concrete type for T.

class Foo<T extends U>

Here, we have added a constraint on the generic type parameter T. You can interpret this as T must be assignable to U.

An example could be

class Foo<T extends any[]>

which specifies that T must be an array.

The final part is

class Foo<T = U>

simply providing a default type parameter if no type is specified when creating an instance of Foo.

Answer 4

Breaking it down into its individual components.

class Foo<T>

This indicates that Foo is a class that accepts a generic type parameter T, nothing too complex here. When you instantiate Foo, you must specify a concrete type for T.

class Foo<T extends U>

Here, we have added a constraint on the generic type parameter T. You can interpret this as T must be assignable to U.

An example could be

class Foo<T extends any[]>

which specifies that T must be an array.

The final part is

class Foo<T = U>

simply providing a default type parameter if no type is specified when creating an instance of Foo.

Understanding the explanation of the function declaration

Answer №1

Answer №2

Similar questions

Angular 2 official launch: Name 'PatternDetails' not found

I am currently working on creating a navigation bar for a webpage using the express framework and pug library. However, when I navigate to the demo page endpoint, the screen appears blank and nothing is displayed

Retrieve the AJAX response, concatenate the data, and construct a dynamic table

Display loading spinners for multiple ajax requests

Angular directive ng-template serves as a component type

Tips for employing multiple reducers with subscribe in Redux (Request for Comments)?

How to retrieve the specific hidden input value in Vue.js that is stored within a div element

Adjusting an item according to a specified pathway

Ask the user through a personalized pop-up window if they want to continue navigating without saving their data

Enhancing web development with jQuery: the power of adding and removing

Tips for breaking out of the loop in Nightwatch when using the '.elements' method

Angular 12's BehaviorSubject should have been empty object array, but it unexpectedly returns undefined

Issue: Unable to load module with AngularJS [GULP CONTEXT]

What are some ways to enhance the speed of swipe and scrolling on mobile devices using Javascript, CSS, and HTML?

Node.js and Express facing challenge with Stripe checkout functionality

Error message: "The toJSON method is not found for the item in the nested array of

The CSS styling for a pie chart does not seem to be functioning properly when using jQuery's

How Mongoose maximizes efficiency with lean usage, populate, and nested queries

Creating a cron job that can be rescheduled using Node.js

Issues with Array.push causing improper pushes