An asynchronous constructor pattern

async-constructor.js

// asynchronous constructor example, 
// like always do not explictly return anything from the constructor

function Queue(){
  
 this.ready = false;
 let callable = true;
 let ee = new EE();    // new event emitter
 // the init method represents our real constructor
 this.init = function (){
    if(this.ready){
         return simpleSyncObservable();  
     }  
    if(!callable){
      // we already called the init method, but aren't yet ready
        return simpleEventObservable(ee);
     } 
     callable = false;
    // we only want to invoke the below chain once
    // whichever method calls it first
    return someObservable()
       .do(() => {
            this.ready = true;
            ee.emit('ready');
         });
   }

}

// every method will probably need to call init() first before anything
Queue.prototype.obs7 = function(){
      // most of our methods start with init()
      return this.init()
           .mapTo(() => 7);
};