NativeScript/packages/core/accessibility/accessibility-service-common.ts

import { Observable } from '../data/observable';

export class SharedA11YObservable extends Observable {
	accessibilityServiceEnabled?: boolean;
}

export const AccessibilityServiceEnabledPropName = 'accessibilityServiceEnabled';

export class CommonA11YServiceEnabledObservable extends SharedA11YObservable {
	constructor(sharedA11YObservable: SharedA11YObservable) {
		super();

		const ref = new WeakRef(this);
		let lastValue: boolean;

		function callback() {
			const self = ref?.get();
			if (!self) {
				sharedA11YObservable.off(Observable.propertyChangeEvent, callback);

				return;
			}

			const newValue = !!sharedA11YObservable.accessibilityServiceEnabled;
			if (newValue !== lastValue) {
				self.set(AccessibilityServiceEnabledPropName, newValue);
				lastValue = newValue;
			}
		}

		sharedA11YObservable.on(Observable.propertyChangeEvent, callback);

		this.set(AccessibilityServiceEnabledPropName, !!sharedA11YObservable.accessibilityServiceEnabled);
	}
}