polygerrit-ui/app/scripts/util.ts

/**
 * @license
 * Copyright (C) 2015 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

export interface CancelablePromise<T> extends Promise<T> {
  cancel(): void;
}

// TODO (dmfilippov): Each function must be exported separately. According to
// the code style guide, a namespacing is not allowed.
export const util = {
  getCookie(name: string) {
    const key = name + '=';
    const cookies = document.cookie.split(';');
    for (let i = 0; i < cookies.length; i++) {
      let c = cookies[i];
      while (c.charAt(0) === ' ') {
        c = c.substring(1);
      }
      if (c.startsWith(key)) {
        return c.substring(key.length, c.length);
      }
    }
    return '';
  },

  /**
   * Make the promise cancelable.
   *
   * Returns a promise with a `cancel()` method wrapped around `promise`.
   * Calling `cancel()` will reject the returned promise with
   * {isCancelled: true} synchronously. If the inner promise for a cancelled
   * promise resolves or rejects this is ignored.
   */
  makeCancelable<T>(promise: Promise<T>) {
    // True if the promise is either resolved or reject (possibly cancelled)
    let isDone = false;

    let rejectPromise: (reason?: unknown) => void;

    const wrappedPromise: CancelablePromise<T> = new Promise(
      (resolve, reject) => {
        rejectPromise = reject;
        promise.then(
          val => {
            if (!isDone) resolve(val);
            isDone = true;
          },
          error => {
            if (!isDone) reject(error);
            isDone = true;
          }
        );
      }
    ) as CancelablePromise<T>;

    wrappedPromise.cancel = () => {
      if (isDone) return;
      rejectPromise({isCanceled: true});
      isDone = true;
    };
    return wrappedPromise;
  },
};