Observable

An implementation of the Observable interfaces as presented in the tc-39 proposal.

How to use

const observable = new Observable.Observable(observer => {
  observer.next(42);
  return () => {};
})

observable.subscribe(value => console.log(value));

outputs:

42

Subject extension

In addition to the interfaces as described in the tc-39 proposal, more convenient interfaces are proposed as the Subject:

const subject = new Observable.Subject();
subject.subscribe({
  next: value => console.log(value),
  error: error => console.log(error),
});
subject.next(42);
subject.error('error!');

outputs:

42
error!

There can be multiple observers to a subject

const subject = new Observable.Subject();
subject.subscribe(value => console.log(`1: ${value}`));
subject.subscribe(value => console.log(`2: ${value}`));
subject.next(42);

outputs:

1: 42
2: 42

BehaviorSubject to attach a variable to a Subject

A BehaviorSubject is a subject that always have a value and which can be queried at any time:

const answer = new Observable.BehaviorSubject(42);
console.log('the answer is:', answer.get());
answer.subscribe(value => console.log('oops, the answer changed:', value));
answer.next(666);

Useful shortcuts

all

all will wait for all the provided observable to have a value and will then forward those values all at once:

import { Observable } from '@jdmichaud/observable'

Observable.all([subject1, subject2], ([value1, value2] =>
  console.log(value1, value2)));
subject1.next(42);
// nothing happens, as subject2 has not yet been triggered.
subject2.next('the answer to everything');
// prints: "42 the answer to everything"
subject1.next(666);
// prints: "666 the answer to everything"

chain

Chains observable in order to smoothly apply processing on next values. Error and complete signals are being forwarded to returned observable. Errors can be raised to the error parameter of the next function parameter:

import { Observable } from '@jdmichaud/observable'

const observable = new Observable<number>(observer => {
  observer.next(42);
  return () => {};
});

let observedValue: string;
// First converts to string.
Observable.chain(observable, value => value.toString()).subscribe({
  next: value => observedValue = value,
});

to

Converts the provided parameters to an observable:

import { Observable } from '@jdmichaud/observable'

Observable.to(1, 2, 3).subscribe(console.log);

from

Converts an array or an iterable to an Observable:

import { Observable } from '@jdmichaud/observable'

const a = [1, 2, 3];
Observable.from(a).subscribe(console.log);