Method update

packages/core/src/createActor.ts:283–354

(snapshot: SnapshotFrom<TLogic>, event: EventObject)

  private _deferred: Array<() => void> = [];

  private update(snapshot: SnapshotFrom<TLogic>, event: EventObject): void {
    // Update state
    this._snapshot = snapshot;

    // Execute deferred effects
    let deferredFn: (typeof this._deferred)[number] | undefined;

    while ((deferredFn = this._deferred.shift())) {
      try {
        deferredFn();
      } catch (err) {
        // this error can only be caught when executing *initial* actions
        // it's the only time when we call actions provided by the user through those deferreds
        // when the actor is already running we always execute them synchronously while transitioning
        // no "builtin deferred" should actually throw an error since they are either safe
        // or the control flow is passed through the mailbox and errors should be caught by the `_process` used by the mailbox
        this._deferred.length = 0;
        this._snapshot = {
          ...(snapshot as any),
          status: 'error',
          error: err
        };
      }
    }

    switch ((this._snapshot as any).status) {
      case 'active':
        for (const observer of this.observers) {
          try {
            observer.next?.(snapshot);
          } catch (err) {
            reportUnhandledError(err);
          }
        }
        break;
      case 'done':
        // next observers are meant to be notified about done snapshots
        // this can be seen as something that is different from how observable work
        // but with observables `complete` callback is called without any arguments
        // it's more ergonomic for XState to treat a done snapshot as a "next" value
        // and the completion event as something that is separate,
        // something that merely follows emitting that done snapshot
        for (const observer of this.observers) {
          try {
            observer.next?.(snapshot);
          } catch (err) {
            reportUnhandledError(err);
          }
        }

        this._stopProcedure();
        this._complete();
        this._doneEvent = createDoneActorEvent(
          this.id,
          (this._snapshot as any).output
        );
        if (this._parent) {
          this.system._relay(this, this._parent, this._doneEvent);