Angular 5 Understanding External Class Imports

Question

I have created a class model for Schedules. I then import this class into my main program. My problem is that this class uses the HttpClient and the way I was taught to use it is to create the variable for it inside the constructor of the class. But the problem then comes in, when I create a new instance of the Schedule (newSchedule = new Schedule;) then it expects a parameter in the place of the HttpClient. How do I make it ignore the HttpClient when I want to create a new instance of the class?

Here is the Schedule model class:

import { HttpClient } from '@angular/common/http';
export class Schedule {
    constructor(private httpClient: HttpClient) {}
}

But now I need to pass this.HttpClient in my main program, which of course is not needed:

import { HttpClient } from '@angular/common/http';
export class AppComponent {
    constructor(private httpClient: HttpClient) {}
    var NewSchedule = new Schedule(this.HttpClient);
}

How do I remove the need to pass this.HttpClient? I assume my process is quite wrong

Answer 1

Your process seems indeed wrong. But you ask for help, so we provide.

You need to make the parameter of the constructor optional. Do like so :

export class Schedule {
  constructor(private http?: HttpClient){}
}

You can also give it a default value :

export class Schedule {
  constructor(private http: HttpClient = null){}
}

Answer 2

After reading the comments, what I understood is, you want to have different instances of the Schedule class but still want to access the httpClient object.

Doing the following may be one solution:

Make a public method under the Schedule class:

public getNewInstance(object: Object) {
    let obj = Object.create(object.constructor.prototype);
    object.constructor.apply(obj, [this.httpClient]);
    return obj;
}

Also make your Subject class injectable. Please note, Your class will be an injectable and an singleton inside another classes, but you will have a way to get several instances using that singleton

DO something like:

@Injectable()
export class Schedule ...

Then, In your appComponent, inject Subject .

export class AppComponent {
constructor(private subjectInstance: Subject) {}
...

private newSubjectInstance;
ngOnInit() {
    this.newSubjectInstance = this.subjectInstance.getNewInstance(this.subjectInstance);
    // so this should be a new instance but still have the httpClent inside it.
}