Struggling to incorporate method decorators to handle http errors in Angular?

My goal is to implement error handling for all http requests using custom decorators. Here's my current code snippet:

  createRecord(data: data) {
    
    return this.httpClient.post(`${this.apiURL}/record/`, data);
  }

I am looking to refactor these functions to incorporate error handling by modifying them like so:

 createRecord(data: data) {
        
        return this.httpClient.post(`${this.apiURL}/record/`, data)
               .pipe(tap((data)=>console.log(data)),catchError(handleError)));
      }

Although I am aware that this can be achieved using http interceptors, I attempted it with custom method decorators instead. The custom decorator I created appears as follows:

export function CatchHttpError() : MethodDecorator {
    return function ( target : any, propertyKey : string, descriptor : PropertyDescriptor ) {
      const original = descriptor.value;
      descriptor.value = original()
      .pipe(
        tap((data)=>console.log('tap entered: data = ',data)),
        catchError(handleError)
      );
      return descriptor;
    };
  }

In order to utilize the decorator, I decorate the function in this manner:

 @CatchHttpError()
  createRecord(data: data) {
    
    return this.httpClient.post(`${this.apiURL}/record/`, data);
  }

The issue here lies in the fact that the function executes upon initializing the service, rather than when calling the createRecord method. How can I adjust the method decorator to achieve the desired behavior?

Answer №1

In order for the decorator to modify how a method behaves when applied, you must replace the original method from within the decorator:

export function CustomizeMethodBehavior() : MethodDecorator {
    return function (target : any, propertyKey : string, descriptor : PropertyDescriptor ) {
      const original = descriptor.value;
      // override the method
      descriptor.value = function(...args: any[]) {
            // Calling the original method
            const originalResults = original.apply(this, args);
            return originalReults.pipe(
                tap((data) => console.log('tap entered: data = ',data)),
                catchError(handleError)
            );
      }
}

It is crucial to use the function keyword instead of an arrow function in defining the override, so that the class context's this can be accessed.

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