Pub Sub in javascript

pub_sub.js

class EventEmitters {
  constructor(){
    this.listeners = new Map();
    this.addListeners = this.addListeners.bind(this);
    this.emit = this.emit.bind(this);
  }
  addListeners(label, callBack){
    let callBacks = [];
    if(this.listeners.has(label)){
      callBacks = this.listeners.get(label);
    }
    callBacks.push(callBack);
    this.listeners.set(label, callBacks);
    console.log(label, this.listeners);
  }
  emit(label){
    console.log(label, this.listeners);
    if(!this.listeners.has(label)) {
      console.error('no listeners found');
    } else {
      const callBacks = this.listeners.get(label);
      callBacks.forEach((cb) => {
        cb();
      });
    }
  }
}

class ModuleA {
  constructor(evt) {
    this.evt = evt
  }

  emitData(){
    this.evt.emit('done');
  }
}

class ModuleB {
  constructor(evt) {
    this.evt = evt
  }
  add(){
    this.evt.addListeners('done', () => {
      console.log('callBack executed');
    })
  }
}

// .. testing methods
const eventObj = new EventEmitters();
const moduleAObj = new ModuleA(eventObj);
const moduleBObj = new ModuleB(eventObj);
moduleBObj.add();
moduleAObj.emitData();

Elegant implementation. You should implement removeListeners and another version for Typescript as well.