Binding a class to an interface

Question

Using typescript, I can easily bind classes to themselves:

bootstrap(MyAppComponent, [MyClass]);

However, I would like to bind my class to

Answer 1

I dont know if it is possible with interface as interface will not be available at runtime (javascript does not know about interface). But it can be done using abstract classes.

//abstract-parent-service.ts

export class DatabaseService{
    getService: ()=>string;
}

//hibernate.service.ts

import {DatabaseService} from "./abstract-parent-service";

export class HibernateService implements DatabaseService{
  constructor() { }
  getService() {
    return "i am hibernate";
  }
}

//jdbc.service.ts

import {DatabaseService} from "./abstract-parent-service";

export class JDBCService implements DatabaseService{
  constructor() { }
  getService() {
    return "i am Jdbc";
  }
}

//cmp-a.component.ts

import {DatabaseService} from "./abstract-parent-service";
import {HibernateService} from "./hibernate.service";

@Component({
    selector: 'cmp-a',
    template: `
Hello Hibernate
`,
    providers: [{provide: DatabaseService, useClass: HibernateService}]
})
export class CmpAComponent {
    constructor (private databaseService: DatabaseService) {
        console.log("Database implementation in CompA :"+this.databaseService.getService());
    }
}

//cmp-b.component.ts

import {DatabaseService} from "./abstract-parent-service";
import {HibernateService} from "./hibernate.service";

@Component({
    selector: 'cmp-b',
    template: `
Hello Jdbc
`,
    providers: [{provide: DatabaseService, useClass: JDBCService}]
})
export class CmpAComponent {
    constructor (private databaseService: DatabaseService) {
        console.log("Database implementation in CompA :"+this.databaseService.getService());
    }
}

But the problem with this implementation is HibernateService and JDBCService are not able to extend any other class now because they have already got married with DatabaseService.

class A{
    constructor(){
        console.log("in A");
    }
}
class B extends A{
    constructor(){
        super();
        console.log("in B");
    }
}
class C extends A{
    constructor(){
        super();
        console.log("in C");
    }
}
let c = new C();

//This thing is not possible in typescript
class D extends B, C{//error:  Classes can only extend a single class
    constructor(){
        super();// which constructor B or C
        console.log("in D");
    }
}

If you are using this pattern for DI, make it sure that your child class services are not going to extend any other functionality in future.