CODEWITHSUNDEEP
javascripttypescript
Get Off My Lawn
Get Off My Lawn

Reputation: 36299

Properties are undefined within a decorator

I am trying to call a function that that has a decorator attached to it. What it does is run every x seconds which works just fine, however, when I try to log the properties in the function they output undefined, but in the constructor it displays the proper class.

If I call another function that is in the class, the function gets called, the issue just seems to be when accessing properties.

Here are a few of the ways I have tried to call the method:

export function Repeat(interval: number, delay: number = 0) {
  return (target: any, prop: any, descriptor: PropertyDescriptor) => {

    timer(delay * 1000, interval * 1000)
      .pipe(
        tap(i => descriptor.value.call(target, i)),
        tap(i => target[prop].call(target, i)),
        tap(i => target[prop].bind(target)(i))
      )
      .subscribe();

  };
}

Here is how I am implementing the decorator:

export class MyClass {

  constructor(private readonly v: Item) { 
    console.log(this.v); // outputs: typeof Item
  }

  @Repeat(1)
  repeat(count: number) {
    console.log(this.v); // outputs: undefined
    this.testFunc(); // runs the function
  }

  testFunc(){
    console.log('test function');
  }
}

Here is a stackblitz example

Edit

After playing for a bit, I can see that I can do this:

export function Repeat(interval: number, delay = 0) {
  return function (target: any, prop: string, descriptor: PropertyDescriptor) {
    const originalMethod = descriptor.value;
    descriptor.value = function (this: GameObject, ...args: any[]) {
      const t = timer(delay * 1000, interval * 1000)
        .pipe(map<number, boolean>(i => originalMethod.apply(this, [i])))
        .subscribe();
    };
    return descriptor;
  };
}

Then when I call it in the class the repeater works:

export class MyClass {

  constructor(private readonly v: Item) { 
    this.repeat(0);
  }

  @Repeat(1)
  repeat(count: number) {
    console.log(this.v); // outputs: typeof Item
  }
}

However, this is not what I want to resort to, I would like the function to be called automatically and not manually.

Upvotes: 3

Views: 597

Answers (1)

Get Off My Lawn
Get Off My Lawn

Reputation: 36299

So, to solve my issue I had to use a decorator at the class level along with at the method level. Then, in the constructor I run the method on the parent class.

First import the reflect-metadata module:

import 'reflect-metadata';

export function Component() {
  return <T extends { new (...args: any[]): any }>(target: T): any => {
    return class extends target {
      private methods: string[] = [];
      constructor(...args: any[]) {
        super(...args);
        this.methods = Reflect.ownKeys(target.prototype) as string[];
        this.runRepeater();
      }

      runRepeater() {
        this.methods.forEach((method) => {
          const { delay, interval } = Reflect.getMetadata('token', target.prototype, method) || {};
          if (!delay || !interval) return;
          timer(delay * 1000, interval * 1000)
            .pipe(map<number, boolean>((i) => super[method]()))
            .subscribe();
        });
      }
    };
  };
}

Here is the repeat function:

export function Repeat(interval: number, delay = 0) {
  return function (target: any, prop: string, descriptor: PropertyDescriptor) {
    Reflect.defineMetadata('token', { interval, delay }, target, prop);
  };
}

Here is how it is implemented in the class:

@Component()
export class MyClass {

  constructor(private readonly v: Item) { 
    console.log(this.v); // outputs: typeof Item
  }

  @Repeat(1)
  repeat(count: number) {
    console.log(this.v); // outputs: typeof Item
  }
}

Here is the stackblitz example.

Upvotes: 2

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