How to define an interface for a class instance using class constructor

Question

I am building a application and part of the code allows developer to specify which component they want to render a certain part. I want users to know they need to implement an interface but I am not sure how to write typing correctly.

export interface ICustomComponent {
    templateObject: any;
}

export class MyComponent implements ICustomComponent {
}

export class MyLib {
    constructor(
        private yourComponent: ICustomComponent
    ) {}
}

new MyLib(MyComponent); <== Fails

I am writing code with Angular, and I cannot run new operator but let Angular to resolve and construct that component.

Here an example that illustrates my problem.

How to deal with this problem?

what do you want to pass here new MyLib(...);? Instance like new MyLib(new MyComponent()); or reference to the class? — Max Koretskyi
– Max Koretskyi, Commented Sep 18, 2017 at 5:02
angular.io/guide/dynamic-component-loader#resolving-components That example is to illustrate the problem only — tom10271
– tom10271, Commented Sep 18, 2017 at 5:11
so do you want to pass MyComponent to componentFactoryResolver.resolveComponentFactory(MyComponent);`? — Max Koretskyi
– Max Koretskyi, Commented Sep 18, 2017 at 5:19
Yes but it is being pass in decorator like @Config({ useComponent: MyComponent }) — tom10271
– tom10271, Commented Sep 18, 2017 at 5:20

Max Koretskyi · Accepted Answer · 2017-09-18 05:49:47Z

2

Since MyLib expects a class constructor, not class instance, you need to define an interface for a class constructor and specify that it returns the instance with the ICustomComponent interface:

interface ICustomComponent {
  templateObject: any;
}

interface ICustomComponentConstructor {
  new (...deps: any[]): ICustomComponent;
}

And then you can use it like this:

export class MyComponent implements ICustomComponent {
  templateObject: any;
}

export class MyLib {
  constructor(private yourComponent: ICustomComponentConstructor) {
  }
}

new MyLib(MyComponent);

You can read about interface for class constructors and instances here.

edited Sep 18, 2017 at 5:49

answered Sep 18, 2017 at 5:35

Max Koretskyi

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