async-await

Ministry of Programming Async/Await Style Guide

Instructions and tips how to use Async/Await

Table of Contents

1. Basic Rules

Basic Rules

• Always use ES7 Async / Await to write asynchronous control flow in code. Do not use another methods to write asynchronous code, Promises, Generators / Yields (ES6)
• Always use bluebird as a promise library

Example 1 - Make simple GET request using request module

• Solution using callbacks

  function getRequest(url, callback) {
    request(url, (error, response, body) => {
      if (error || response.statusCode !== 200) {
        callback(error || new Error(response.statusCode));
      } else {
        callback(null, body);
      }
    });
  }
  
  getRequest('https://httpbin.org/ip', (error, body) => {
    if (error) {
      console.error(error);
    } else {
      console.log(body);
    }
  });

• Solution using async/await

  function getRequest(url) {
    return new Promise((resolve, reject) => {
      request(url, (error, response, body) => {
        if (error || response.statusCode !== 200) {
          reject(error || new Error(response.statusCode));
        } else {
          resolve(body);
        }
      });
    });
  }
  
  async function test() {
    try {
      const body = await getRequest('https://httpbin.org/ip');
      console.log(body);
    } catch (err) {
      console.error(err);
    }
  }
  
  test();

Example 2 - Make multiple GET requests using request module

Get list of posts from RESTful API and get comments for first post

• Solution using callbacks

  function getRequest(url, callback) {
    request(url, (error, response, body) => {
      if (error || response.statusCode !== 200) {
        callback(error || new Error(response.statusCode));
      } else {
        callback(null, body);
      }
    });
  }
  
  const apiUrl = 'http://jsonplaceholder.typicode.com';
  getRequest(`${apiUrl}/posts`, (errPosts, bodyPosts) => {
    if (errPosts) {
      console.error(errPosts);
    } else {
      const firstPost = JSON.parse(bodyPosts)[0];
      console.log(`Post title: ${firstPost.title}`);
  
      getRequest(`${apiUrl}/posts/${firstPost.id}/comments`, (errComments, bodyComments) => {
        if (errComments) {
          console.error(errComments);
        } else {
          const comments = JSON.parse(bodyComments);
          console.log(`Comments count: ${comments.length}`);
        }
      });
    }
  });

• Solution using async/await

  function getRequest(url) {
    return new Promise((resolve, reject) => {
      request(url, (error, response, body) => {
        if (error || response.statusCode !== 200) {
          reject(error || new Error(response.statusCode));
        } else {
          resolve(body);
        }
      });
    });
  }
  
  async function test() {
    const apiUrl = 'http://jsonplaceholder.typicode.com';
    try {
      const bodyPosts = await getRequest(`${apiUrl}/posts`);
      const firstPost = JSON.parse(bodyPosts)[0];
      console.log(`Post title: ${firstPost.title}`);
  
      const bodyComments = await getRequest(`${apiUrl}/posts/${firstPost.id}/comments`);
      const comments = JSON.parse(bodyComments);
      console.log(`Comments count: ${comments.length}`);
    } catch (err) {
      console.error(err);
    }
  }
  
  test();