Exploring the differences between Typescript decorators and class inheritance

Question

Exploring the differences between Typescript decorators and class inheritance

I find myself puzzled by the concept of typescript decorators and their purpose. It is said that they 'decorate' a class by attaching metadata to it. However, I am struggling to understand how this metadata is linked to an instance of the class. An example provided is in Angular 2.

 @Component(
       {
          selector:...
       }
    ) 


    export class foo { ... }

My current understanding is that Angular instantiates the foo class and somehow connects the instance with the arguments of the decorator so that it can offer services, directives, and templates. This functionality could potentially be achieved through class inheritance as well. If we have a Component class and have our component inherit from it, why couldn't Angular then pass those arguments during bootstrapping similar to how React handles props, eliminating the need for decorators in such cases?

class Component { ... } //assume members like selector, services, directives, etc..

class Foo extends Component { ... }

then you would instantiate it at bootstrap/runtime using this approach:

new Foo(ElementName, Directives, Services, etc..)

In React, this process was essentially happening behind the scenes. You extended a component and utilized its methods. When passing information upon instantiation, you would provide the props object.

I'm eager to gain further insight on this matter.

typescript angular decorator

Answer 1

Answer №1

It's interesting how this code bears resemblance:

import { Component } from '@angular/core';
export class AppComponent extends Component{ }

VS:

import { Component } from '@angular/core';
@Component()
export class AppComponent { }

When it comes to inheritance in JS, there are various approaches - if you choose to utilize the Class syntactic sugar and opt for the extends syntax for implementing inheritance, then you're limited to single inheritance - meaning each class can only inherit from one other class.

Using Decorators, on the other hand, allows for attaching multiple behaviors to a class, enabling multiple inheritance similar to mixins. As Günter Zöchbauer mentioned, decorators are much more static in evaluation compared to runtime evaluation required by inheritance.

I see Decorators as a form of composition - since they are essentially functions, I perceive them akin to higher-order functions, making the code more readable:

import { Component } from '@functionalComponent/core';
let myComponent = function() { return {hello: 'world'}}
let AppComponent = Component(myComponent())

It's crucial to remember that a Class is fundamentally a pure JS object, instantiated through a constructor function.

import { Component } from '@constructedComponent/core';
let MyComponent = function() {this.hello ='world'}
let AppComponent = new Component(new MyComponent)

Alternatively, you can think of it on a lower level, treating it purely as objects:

import { Component } from '@objectComponent/core';
let MyComponent = {this.hello ='world'}
let AppComponent = Component.augment(MyComponent)

The prototypal and functional aspects of JS offer great flexibility for mixing behavior through function calls and object alterations. However, once you shift to the Class syntax, it's advisable to adhere to the OOP design principle of Composition over inheritance, with decorators providing a clear and readable way to express composition:

Difference between the Composite Pattern and Decorator Pattern?

As stated on Wikipedia:

Decorator use can be more efficient than subclassing, because an objects behavior can be augmented without instantiating an entirely new object.

Answer 2

It's interesting how this code bears resemblance:

import { Component } from '@angular/core';
export class AppComponent extends Component{ }

VS:

import { Component } from '@angular/core';
@Component()
export class AppComponent { }

When it comes to inheritance in JS, there are various approaches - if you choose to utilize the Class syntactic sugar and opt for the extends syntax for implementing inheritance, then you're limited to single inheritance - meaning each class can only inherit from one other class.

Using Decorators, on the other hand, allows for attaching multiple behaviors to a class, enabling multiple inheritance similar to mixins. As Günter Zöchbauer mentioned, decorators are much more static in evaluation compared to runtime evaluation required by inheritance.

I see Decorators as a form of composition - since they are essentially functions, I perceive them akin to higher-order functions, making the code more readable:

import { Component } from '@functionalComponent/core';
let myComponent = function() { return {hello: 'world'}}
let AppComponent = Component(myComponent())

It's crucial to remember that a Class is fundamentally a pure JS object, instantiated through a constructor function.

import { Component } from '@constructedComponent/core';
let MyComponent = function() {this.hello ='world'}
let AppComponent = new Component(new MyComponent)

Alternatively, you can think of it on a lower level, treating it purely as objects:

import { Component } from '@objectComponent/core';
let MyComponent = {this.hello ='world'}
let AppComponent = Component.augment(MyComponent)

The prototypal and functional aspects of JS offer great flexibility for mixing behavior through function calls and object alterations. However, once you shift to the Class syntax, it's advisable to adhere to the OOP design principle of Composition over inheritance, with decorators providing a clear and readable way to express composition:

Difference between the Composite Pattern and Decorator Pattern?

As stated on Wikipedia:

Decorator use can be more efficient than subclassing, because an objects behavior can be augmented without instantiating an entirely new object.

Answer 3

Answer №2

One of the primary reasons for including metadata in Angular components is to simplify static evaluation. In the absence of metadata, executing TypeScript or transpiled JavaScript code would be necessary to obtain relevant information.

By evaluating this metadata statically, various tools can utilize it for purposes such as autocompletion, lint checks within templates, and facilitating the creation of designers and other resources that streamline the development of Angular applications.

Additionally, the offline template compiler relies on this metadata for efficient compilation.

Answer 4

One of the primary reasons for including metadata in Angular components is to simplify static evaluation. In the absence of metadata, executing TypeScript or transpiled JavaScript code would be necessary to obtain relevant information.

By evaluating this metadata statically, various tools can utilize it for purposes such as autocompletion, lint checks within templates, and facilitating the creation of designers and other resources that streamline the development of Angular applications.

Additionally, the offline template compiler relies on this metadata for efficient compilation.

Exploring the differences between Typescript decorators and class inheritance

Answer №1

Answer №2

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