Learn TypeScript 3 by Building Web Applications

RxJS basics − observers

Creating observables is only half the battle. Having a data source is one thing, but if nobody observes, listens, or watches, then it is pretty much useless. As a matter of fact, an observable will only be executed if there is at least one observer.

With RxJS, each subscriber is called Observer. These are listeners for the values emitted/produced by Observable.

Here's a basic example:

const observer = { 
    next: (x:any) => console.log(`Observer got a next value: ${x}`), 
    error: (err:any) => console.error(`Observer got an error: ${err}`), 
    complete: () => console.log('Observer got a completion notification') 
}; 

Here, the observer object is a valid observer. As illustrated in the preceding code block, it should have three ...