Angular - How to combine multiple "valueChanges" observables into one

Question

How can I combine the following subscriptions into one?

    this.form.get("type").valueChanges.subscribe(() => {
        this.calcFinalTransports();
    })
    this.form.get("departure").valueChanges.subscribe(() => {
        this.calcFinalTransports();
    })
    this.form.get("destination").valueChanges.subscribe(() => {
        this.calcFinalTransports();
    })
    this.form.get("stations").valueChanges.subscribe(() => {
        this.calcFinalTransports();
    })

Answer 1

You have a few choices depending on what output you expect. You may want to read this article:

• Learn to combine RxJs sequences with super intuitive interactive diagrams

If you just want to get notified whenever any of the value changes use merge:

import {merge} from "rxjs/observable/merge";

merge(
    this.form.get("type").valueChanges,
    this.form.get("departure").valueChanges,
    this.form.get("destination").valueChanges
    this.form.get("stations").valueChanges
).subscribe(() => this.calcFinalTransports());