/**
* 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;
}
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