Example of how publishReplay works

publishReplay.js

// https://jsbin.com/gacexawuju/edit?js,console

//emit value every 1 second
const source = Rx.Observable.interval(1000).take(5);
const example = source
  //side effects will be executed once
  .do(() => console.log('Do Something!'))
  //do nothing until connect() is called
  // Cache the last 3 values
  .publishReplay(3)

/*
  source will not emit values until connect() is called
  output: (after 2s) 
  "Do Something!"
  "Subscriber One: 0"
  "Do Something!"
  "Subscriber One: 1"
  "Do Something!"
  "Subscriber One: 2"
  "Do Something!"
  "Subscriber One: 3"
  "Do Something!"
  "Subscriber One: 4"
  "Subscriber Two: 2"
  "Subscriber Two: 3"
  "Subscriber Two: 4"
*/
const subscribe = example.subscribe(val => console.log(`Subscriber One: ${val}`));

//call connect after 5 seconds, causing source to begin emitting items
setTimeout(() => {
 example.connect(); 
},2000)

setTimeout(() => {
  example.subscribe(val => console.log(`Subscriber Two: ${val}`));
},7500)