TS - decorator relies on another irrespective of their position within the class

Question

TS - decorator relies on another irrespective of their position within the class

Is it possible to consistently run function decorator @A before @B, regardless of their position within the class?


class Example {

@A()
public method1(): void { ... }

@B()
public method2(): void { ... }

@A()
public method3(): void { ... }

}

In the scenario above, I am seeking to ensure that the @A decorators for method1 and method3 are executed prior to @B() no matter where the methods are located in the class.

typescript decorator typescript-decorator

Answer 1

Answer №1

I discovered a clever technique using ReflectMetadata:

A special decorator


export const A =
  () =>
  (consumer: any, methodName: string, descriptor: PropertyDescriptor) => {
    const existingAMethods =
      Reflect.getOwnMetadata("A_METHODS", consumer.constructor) || []
    const options: {
      consumer,
      methodName,
      descriptor
    }
    existingAMethods.push(options)
    Reflect.defineMetadata(
      "A_METHODS",
      existingAMethods,
      consumer.constructor
    )
  }

Another unique decorator


export const B =
  () =>
  (consumer: any, methodName: string, descriptor: PropertyDescriptor) => {
    const existingBMethods =
      Reflect.getOwnMetadata("B_METHODS", consumer.constructor) || []
    const options: {
      consumer,
      methodName,
      descriptor
    }
    existingBMethods.push(options)
    Reflect.defineMetadata(
      "B_METHODS",
      existingBMethods,
      consumer.constructor
    )
  }

Introducing the final one called "C"

export const C = () =>
  (constructor: Function): void => {
    const options =
      Reflect.getOwnMetadata("A_METHODS", constructor) || []
    // Perform actions related to A
    const options =
      Reflect.getOwnMetadata("B_METHODS", constructor) || []
    // Perform actions related to B
  }

Application example

@C()
class Example {

  @A()
  public method1(): void { ... }

  @B()
  public method2(): void { ... }

  @A()
  public method3(): void { ... }

}

Answer 2

I discovered a clever technique using ReflectMetadata:

A special decorator


export const A =
  () =>
  (consumer: any, methodName: string, descriptor: PropertyDescriptor) => {
    const existingAMethods =
      Reflect.getOwnMetadata("A_METHODS", consumer.constructor) || []
    const options: {
      consumer,
      methodName,
      descriptor
    }
    existingAMethods.push(options)
    Reflect.defineMetadata(
      "A_METHODS",
      existingAMethods,
      consumer.constructor
    )
  }

Another unique decorator


export const B =
  () =>
  (consumer: any, methodName: string, descriptor: PropertyDescriptor) => {
    const existingBMethods =
      Reflect.getOwnMetadata("B_METHODS", consumer.constructor) || []
    const options: {
      consumer,
      methodName,
      descriptor
    }
    existingBMethods.push(options)
    Reflect.defineMetadata(
      "B_METHODS",
      existingBMethods,
      consumer.constructor
    )
  }

Introducing the final one called "C"

export const C = () =>
  (constructor: Function): void => {
    const options =
      Reflect.getOwnMetadata("A_METHODS", constructor) || []
    // Perform actions related to A
    const options =
      Reflect.getOwnMetadata("B_METHODS", constructor) || []
    // Perform actions related to B
  }

Application example

@C()
class Example {

  @A()
  public method1(): void { ... }

  @B()
  public method2(): void { ... }

  @A()
  public method3(): void { ... }

}

TS - decorator relies on another irrespective of their position within the class

Answer №1

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