material-web/controller/observer-foundation.ts

/**
 * @license
 * Copyright 2021 Google LLC
 * SPDX-License-Identifier: Apache-2.0
 */

import {Foundation} from './foundation';
import {observeProperty, ObserverRecord} from './observer';

/**
 * Legacy observer foundation class for components.
 */
export class ObserverFoundation<Adapter extends object> extends
    Foundation<Adapter> {
  /**
   * Observe a target's properties for changes using the provided map of
   * property names and observer functions.
   *
   * @template T The target type.
   * @param target - The target to observe.
   * @param observers - An object whose keys are target properties and values
   *     are observer functions that are called when the associated property
   *     changes.
   * @return A cleanup function that can be called to unobserve the
   *     target.
   */
  protected observe<T extends object>(
      target: T, observers: ObserverRecord<T, this>) {
    const cleanup: Function[] = [];
    for (const property of Object.keys(observers) as Array<keyof T>) {
      const observer = observers[property]!.bind(this);
      cleanup.push(observeProperty(target, property, observer));
    }

    return () => {
      for (const cleanupFn of cleanup) {
        cleanupFn();
      }
    };
  }
}