# All files / util node_api.ts

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     /**
     * Copyright 2017 Google Inc.
     *
     * 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.
     */

    import { AnyJs } from './misc';

    /*
     * Utilities for dealing with node.js-style APIs. See nodePromise for more
     * details.
     */

    /**
     * Creates a node-style callback that resolves or rejects a new Promise. The
     * callback is passed to the given action which can then use the callback as
     * a parameter to a node-style function.
     *
     * The intent is to directly bridge a node-style function (which takes a
     * callback) into a Promise without manually converting between the node-style
     * callback and the promise at each call.
     *
     * In effect it allows you to convert:
     *
     * @example
     * new Promise((resolve: (value?: fs.Stats) => void,
     *              reject: (error?: any) => void) => {
     *   fs.stat(path, (error?: any, stat?: fs.Stats) => {
     *     if (error) {
     *       reject(error);
     *     } else {
     *       resolve(stat);
     *     }
     *   });
     * });
     *
     * Into
     * @example
     * nodePromise((callback: NodeCallback<fs.Stats>) => {
     *   fs.stat(path, callback);
     * });
     *
     * @param action a function that takes a node-style callback as an argument and
     *     then uses that callback to invoke some node-style API.
     * @return a new Promise which will be rejected if the callback is given the
     *     first Error parameter or will resolve to the value given otherwise.
     */
    export function nodePromise<R>(
      action: (callback: NodeCallback<R>) => void
    ): Promise<R> {
      return new Promise(
        (resolve: (value?: R) => void, reject: (error?: AnyJs) => void) => {
          action((error?: AnyJs, value?: R) => {
            if (error) {
              reject(error);
            } else {
              resolve(value);
            }
          });
        }
      );
    }

    /**
     * A node-style callback which passes an Error as the first argument if there
     * was an error, or passes null and a proper value
     */
    export interface NodeCallback<R> {
      (error?: AnyJs, value?: R): void;
    }