Enhancing Angular 6 with Constructor Overloading

I'm a newcomer to TypeScript/Angular and I have a constructor set up to fetch JsonP. Now, I want to add a new constructor for HttpClientModule. Here's my current code:

export class DataService {
    constructor(private _jsonp: Jsonp) {
        this.apikey = 'xxx';
    }
}

This is what I attempted:

export class DataService {
    constructor(private _jsonp: Jsonp, private http: HttpClient) {
        this.apikey = 'xxx';
    }
}

However, the initial JSON API stops working. I am looking for an equivalent solution like this:

export class DataService {
    constructor(private _jsonp: Jsonp) {
        this.apikey = 'xxx';
    }
    constructor(http: HttpClient) {}
}

Answer №1

If you were to tackle this problem in Typescript, the approach might resemble the example below. Essentially, you first define the method signatures and then proceed to implement them (ensuring that all possible scenarios are accounted for).

export class DataService {
    constructor(private _jsonp: Jsonp);
    constructor(http: HttpClient);

    // Constructor implementation
    constructor(api: Jsonp | HttpClient){
        // Determine the type of the parameter through some form of test
        if (/* api is Jsonp */) {
            // Handle the case where api is a Jsonp instance, not an HttpClient instance
            this.apikey = 'xxx';
        }
    }
}

Answer №2

When working with TypeScript, it is important to note that overloading is a feature that can be utilized. For more information on this topic, refer to the following question: Constructor overload in TypeScript

Another commonly seen practice involves providing an optional parameter when defining functions that may include various options. This approach can look something like the example provided below:

export class DataService {
  constructor(private _jsonp: Jsonp, private http: HttpClient) {
    this.apikey = 'xxx';
  }

  get(params?, options?) {
    if (this.options && this.options.service === 'jsonp') {
     // utilize the _jsonp service
    } else {
     // utilize the http service
    }
  }
}

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