Subscribe to Observables in order but only when the previous completes, let me know, then move to the next one. Use this operator when the order is important, for example when you need to send HTTP requests that should be in order. 2. forkJoin —forkJoin is the Promise.all() of Rx. Don’t let me know until all the Observables are complete, then give me all the values at once. ( Array ) First, let’s