How to include class definition through “this” keyword in Typescript?

Asked By: Anonymous

I’m creating a class that extend HttpClient then extending this keyword through includeEventsIn function, includeEventsIn will extend BaseService with EventAggregator type, see code here.

Question

• How can I include EventAggregator methods and props in BaseService class along with HttpClient?
• What would be another approach to extend class(BaseService) with two class?

Here’s the code.

@transient()
export class BaseService extends HttpClient {
    constructor() {
        super();
        includeEventsIn(this);
    }
}

Solution

Answered By: Anonymous

You shouldn’t use inheritance when building Aurelia apps unless absolutely necessary (and I would argue it’s never necessary). Favor composition over inheritance.

For example, in your case, I would have Service (not BaseService, because you would no longer be using inheritance) take a dependency on HttpClient and EventAggregator. I doubt you truly need all of the functionality that gets added by the call to includeEventsIn. That being said, if you do need it, then you can simply add the three functions to Service.

import {inject, EventAggregator} from 'aurelia-framework';
import {HttpClient} from 'aurelia-fetch-client';

@inject(HttpClient, EventAggregator)
export class Service {
  constructor( http, ea ) {
    this.http = http;
    this.ea = ea;
  }
}

You can then inject this class in to another class as needed, after implementing whatever functionality it needs.