States

Umbraco States enables you to create Observables based on a State. The Observables can then be observed, and when a change to the State occurs, all observers of Observables will be triggered.

State types

Umbraco comes with a State type for the most common types of data:

• Array State

• Boolean State

• Class State

• Number State

• Object State

• String State

Observables

Observe a state via Umbraco Element or Umbraco Controller

The Umbraco Element or Controllers comes with the ability to observe an Observable.

While observing all changes will result in the callback being executed.

The example below creates a State and then turns the whole state into an Observable, which then can be observed.

import { UmbArrayState } from '@umbraco-cms/backoffice/observable-api';

...

this.#selectionState = UmbArrayState<string>(['item1', 'item2']);
this.selection = this.#selectionState.asObservable();

this.observe(
	this.selection,
	(selection) => {
		// This call will be executed initially and on each change of the state
	}
);

Change the value of a state

The value of a state can be changed via the setValue method. This replaces the current data with new data.

The following example shows how to change the value of the state to hold item2 and item3. As the example extends the example from above, it means that item1 is no longer part of the value of this state.

import { UmbArrayState } from '@umbraco-cms/backoffice/observable-api';

...

this.#selectionState.setValue(['item2', 'item3']);

Observe part of a state

With the asObservablePart method, you can set up an Observable that provides a transformed outcome, based on the State.

this.selectionLength = this.#selectionState.asObservablePart(data => data.length);

this.observe(
    this.selectionLength, (length) => {
        // This call will be executed, initially and on each change of the specific value that this observer provides.
        // This means that this will only be executed when the length changed. Not if the value was replaced with a new value value with the exact same length.
        console.log("Length of selection is now ", length)
	}
);

In the above example, the asObservablePart mapping function will be executed every time there is a change to the State. If the result of the method is different than before it will trigger an update to its observers.