The Observable Triad

ACTIONS ==> OBSERVABLES ==> REACTIONS

Observables

• Concept of reactive-data
• Various decorators to simplify marking properties as observables
  • @observable
  • observable.ref
  • observable.shallow
• Can be applied to objects, arrays and maps
• Always use classes. Occassionally rely on decorate() or extendObservable()
• Computed properties
  • Also called Derivations, Derived properties
  • Think of your reactive-data as a combination of Core Observables + Derived Observables (Computed)
  • Reactions in disguise
  • Used as decorator: @computed

Actions

• Adds vocabulary of operations and makes it very Domain Driven
• Transactional notifications to changes in observables
• Most often used with decorators: @action
• configure({enforceActions: 'never' | 'observed' | 'always'})
• Use of runInAction(() => {}) to wrap mutations after an async call

Reactions

• These are the observers in the system.
• Of 3 kinds: autorun(), reaction(), when()
• Each returns a disposer which can be used to prematurely stop the observation
• UI is modeled as reaction()

autorun()

• Long running
• No way to select the observables explicitly
• Selector + Effect function is combined into one

autorun(() => {
    const { name, email } = this;
    validate({ name, email }, rules);
});

reaction()

• Long running
• First argument is a selector function
• Second argument is the effect function

reaction(() => this.isComplete, () => this.notifyServer());

Options for autorun and reaction

• delay can be used to debounce the side-effect for both autorun() and reaction()
• More options available like name, onError, etc.

when()

• One time only
• Automatically dispose after completion of side-effect
• First argument is a predicate function
• When it becomes true, the side-effect is executed

when() with promise

• Used as a promise to await and run the side-effect as a continuation. Handy way to mark junctions in your logic.

async function showAlertOnExpirty() {
    await when(() => this.hasOfferExpired);

    showAlert('Offer Expired');
}

Other helpful tools and libraries

mobx-react-devtools

mobx-utils

• fromPromise()
• createViewModel()

mobx-state-tree