web/cache-object.ts

// Copyright 2018 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
const localStorage = window.localStorage;

/** A localStorage-backed cached JSON object. */
export class CacheObject {
  key: string;

  /**
   * Creates a new CacheObject instance.
   *
   * @param key localStorage key name for storage.
   */
  constructor(key: string) {
    this.key = key;
  }

  private checkObj(obj: any) {
    if (typeof obj !== 'object' || Array.isArray(obj)) {
      throw Error('obj parameter value is not an Object');
    }
    return obj;
  }

  /**
   * Reads the cached object.
   *
   * @return The object from storage.
   *   On failure, clears the storage and returns {}.
   */
  read(): any {
    try {
      const storeItem = localStorage.getItem(this.key);
      if (storeItem == null) {
        return {};
      }
      return this.checkObj(JSON.parse(storeItem));
    } catch (ex) {
      console.warn(
        `error while reading cache at localStorage key "${this.key}`,
        ex
      );
      localStorage.removeItem(this.key);
      return {};
    }
  }

  /** Writes the cache value. */
  write(obj: any) {
    localStorage.setItem(this.key, JSON.stringify(this.checkObj(obj)));
  }

  /** Clears the cache value. */
  clear() {
    localStorage.removeItem(this.key);
  }
}