can we somehow pass the parameter string inside constructor of interceptor in nestjs, making it more general and configurable?

I am using the following interceptor to transform the gameLevel from string to number.

@Injectable()
export class EnumStringToNumberInterceptor implements NestInterceptor {
    constructor() {}
    intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
        return next.handle().pipe(map(data => {
            if (data && data.list) {
                data.list.forEach(d => {
                    d['gameLevel'] = Number(d['gameLevel']);
                })
            } else if (data && data.gameLevel) {
                data['gameLevel'] = Number(data['gameLevel']);
            }
            return data;
        }));
      }
}

I want to pass gameLevel as key somehow in constructor something like the following –

constructor(private readonly key: string) {}

// and do something like this
d[key] = Number(d[key]);

By achieving this I will be making this interceptor more general to use it in different such use cases when key will be differing.

>Solution :

If you have nothing being injected into the interceptor, then a simple new Interceptor('key or whatever string') works well.

If you do have something being injected, I would suggest making use of reflection and following Nest’s docs on setting up custom metadata that the interceptor can read at runtime.

Something along the lines of

export const GameLevel = (key: string) => SetMetadata('GAME_LEVEL_METADATA', key);

Then in your controller you can use @GameLevel('someLevelKey') and in the interceptor you can do something along the lines of

@Injectable()
export class EnumStringToNumberInterceptor implements NestInterceptor {
    constructor(private readonly reflector: Reflector) {}
    intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
        const level = this.reflector.getAllAndOverride('GAME_LEVEL_METADAT', [context.getClass(), context.getHandler()]);
        return next.handle().pipe(map(data => {
            if (data && data.list) {
                data.list.forEach(d => {
                    d[level] = Number(d[level]);
                })
            } else if (data && data[level]) {
                data[level] = Number(data[level]);
            }
            return data;
        }));
      }
}