Rxjs-example.ts

emitValue(observer) {  
    let i = 0;
       const id = setInterval(() => {
           observer.next(i++)
       }, 1000)
       return () => { clearInterval(id) }
   } 

   createObservable(emitValueFn) {
       return {
           subscribe: emitValueFn,
       }
   }

   const observer = { next: (v) => { console.log(v) }}
   const observable = createObservable(emitValue);
   const unsubscribe = observable.subscribe(observer)

   setTimeout(() => {
     unsubscribe()
   }, 4500)

really concrete example, thanks