TypeScript Error On Implementing Interface

Question

Compiler Error-

Class 'MessageBus' incorrectly implements interface 'IMessageBus'. Property 'dispatch' is missing in type 'MessageBus'.

IMessageBus Interface-

export interface IMessageBus {
  dispatch: (eventName: string, info?: any) => void;
  listen: (eventName: string, callback: Function) => void;
}

MessageBus Class-

import {IMessageBus} from './IMessageBus';

export class MessageBus implements IMessageBus {
  static listeners: Object[] = [];
  public static dispatch(event: string, info?: any): void {
     this.listeners
        .forEach((l) => {
           if (l["event"] === event) {
               l["cb"](info);
           }
        });
  }

  public static listen(event:string, cb: (any) => any):void {
    this.listeners.push({event: event, cb: cb});
  }
}

Please advice on how to resolve this.

stackoverflow.com/questions/20992514/…

shiv
– shiv

2016-03-23 12:27:34 +00:00
Commented Mar 23, 2016 at 12:27 — shiv
– shiv, Commented Mar 23, 2016 at 12:27

Martin · Accepted Answer · 2016-03-23 10:34:23Z

3

Thierry's answer is correct.

Your interface is not defined wrong. But a more idiomatic definition would look like:

export interface IMessageBus {
  dispatch(eventName: string, info?: any): void;
  listen(eventName: string, callback: Function): void;
}

answered Mar 23, 2016 at 10:34

Martin

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Comments

Thierry Templier · Accepted Answer · 2016-03-23 09:51:29Z

2

I think that you should remove the static keyword for your methods in the class implementing the interface:

export class MessageBus implements IMessageBus {
  listeners: Object[] = [];
  public dispatch(event: string, info?: any): void {
    this.listeners
      .forEach((l) => {
        if (l["event"] === event) {
           l["cb"](info);
        }
      });
  }

  public listen(event:string, cb: (any) => any):void {
    this.listeners.push({event: event, cb: cb});
  }
}

answered Mar 23, 2016 at 9:51

Thierry Templier

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2 Comments

shiv Over a year ago

Hi Thierry, Thanks for the reply. Although I am not looking to instantiate new instance of MessageBus. Hence the need for static. This should do the trick. stackoverflow.com/questions/20992514/…

Thierry Templier Over a year ago

Hey. I see the problem. Yes, this question is definitely what you're looking for. I didn't know the "assign the class to the interface" feature of TypeScript. But it's a cool one ;-)

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