Exploring the realm of Typescript custom decorators: The significance behind context

Question

Exploring the realm of Typescript custom decorators: The significance behind context

I'm currently working on a custom decorator that will execute decorated functions based on RxJS events.

Everything seems to be going well so far, but I'm facing an issue when the function is executed: the context of the this object is lost.

I've been searching for a solution for the past day without any luck.

If you want to check out the problem, you can view a stackblitz example here. The objective is to see "Angular" in the console, coming from this.name.

angular typescript decorator aop

Answer 1

Answer №1

It appears that you are attempting to invoke a method on the instance of a decorated class within your decorator. However, it's important to note that class decorators operate differently. They are executed during the class definition process, not during instantiation. As a result, calling methods with instances of your class is not supported by class decorators.

You can access the updated stackblitz here. In this version, I have extended your class and invoked the method in the constructor of the extended class. This ensures that the method is called whenever objects of the decorated class are instantiated.

Answer 2

It appears that you are attempting to invoke a method on the instance of a decorated class within your decorator. However, it's important to note that class decorators operate differently. They are executed during the class definition process, not during instantiation. As a result, calling methods with instances of your class is not supported by class decorators.

You can access the updated stackblitz here. In this version, I have extended your class and invoked the method in the constructor of the extended class. This ensures that the method is called whenever objects of the decorated class are instantiated.

Answer 3

Answer №2

Give this code a try, it should function properly. Simply replace 'HelloWorld' with 'constructor'.

function Greetings(): ClassDecorator {
  return function(constructor) {
    constructor.prototype.Greetings.apply(new constructor(), null);
  };
}

Answer 4

Give this code a try, it should function properly. Simply replace 'HelloWorld' with 'constructor'.

function Greetings(): ClassDecorator {
  return function(constructor) {
    constructor.prototype.Greetings.apply(new constructor(), null);
  };
}

Answer 5

Answer №3

My unique way of explaining how context is conveyed in a method using map :)

return class extends constructor {
            constructor(...args) {
                super(...args);
                if(constructor.processCallbackMap){
                    Array.from(constructor.processCallbackMap).map(([key, value]) = {
                        constructor.processCallbackMap.set(key, value.bind(this));
                    });
                }
            }
        }

Answer 6

My unique way of explaining how context is conveyed in a method using map :)

return class extends constructor {
            constructor(...args) {
                super(...args);
                if(constructor.processCallbackMap){
                    Array.from(constructor.processCallbackMap).map(([key, value]) = {
                        constructor.processCallbackMap.set(key, value.bind(this));
                    });
                }
            }
        }

Answer 7

Answer №4

Check out this article for some custom decorator inspiration in Angular:

When you comment out the line below, your app will work fine:
constructor.prototype.HelloWord.apply(this, null);

The constructor.prototype is utilized to enable the use of ngOnInit, ngOnChanges, and more.

For example, the code snippet on the page shows how to create a function called NgLog:

import { environment } from "../environments/environment";
export function NgLog() : ClassDecorator {
  return function ( constructor : any ) {
    if( !environment.production ) {
      // You can add/remove events for your needs
      const LIFECYCLE_HOOKS = [
        'ngOnInit',
        'ngOnChanges',
        'ngOnDestroy'
      ];
      const component = constructor.name;

      LIFECYCLE_HOOKS.forEach(hook => {
        const original = constructor.prototype[hook];

        constructor.prototype[hook] = function ( ...args ) {
          console.log(`%c ${component} - ${hook}`, `color: #4CAF50; font-weight: bold`, ...args);
          original && original.apply(this, args);
        }
      });
    }

  }
}

Answer 8

Check out this article for some custom decorator inspiration in Angular:

When you comment out the line below, your app will work fine:
constructor.prototype.HelloWord.apply(this, null);

The constructor.prototype is utilized to enable the use of ngOnInit, ngOnChanges, and more.

For example, the code snippet on the page shows how to create a function called NgLog:

import { environment } from "../environments/environment";
export function NgLog() : ClassDecorator {
  return function ( constructor : any ) {
    if( !environment.production ) {
      // You can add/remove events for your needs
      const LIFECYCLE_HOOKS = [
        'ngOnInit',
        'ngOnChanges',
        'ngOnDestroy'
      ];
      const component = constructor.name;

      LIFECYCLE_HOOKS.forEach(hook => {
        const original = constructor.prototype[hook];

        constructor.prototype[hook] = function ( ...args ) {
          console.log(`%c ${component} - ${hook}`, `color: #4CAF50; font-weight: bold`, ...args);
          original && original.apply(this, args);
        }
      });
    }

  }
}

Exploring the realm of Typescript custom decorators: The significance behind context

Answer №1

Answer №2

Answer №3

Answer №4

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