Table of Contents for
Node.js 8 the Right Way

Version ebook / Retour

Cover image for bash Cookbook, 2nd Edition Node.js 8 the Right Way by Jim Wilson Published by Pragmatic Bookshelf, 2018
  1. Title Page
  2. Node.js 8 the Right Way
  3. Node.js 8 the Right Way
  4. Node.js 8 the Right Way
  5. Node.js 8 the Right Way
  6.  Acknowledgments
  7.  Preface
  8. Why Node.js the Right Way?
  9. What’s in This Book
  10. What This Book Is Not
  11. Code Examples and Conventions
  12. Online Resources
  13. Part I. Getting Up to Speed on Node.js 8
  14. 1. Getting Started
  15. Thinking Beyond the web
  16. Node.js’s Niche
  17. How Node.js Applications Work
  18. Aspects of Node.js Development
  19. Installing Node.js
  20. 2. Wrangling the File System
  21. Programming for the Node.js Event Loop
  22. Spawning a Child Process
  23. Capturing Data from an EventEmitter
  24. Reading and Writing Files Asynchronously
  25. The Two Phases of a Node.js Program
  26. Wrapping Up
  27. 3. Networking with Sockets
  28. Listening for Socket Connections
  29. Implementing a Messaging Protocol
  30. Creating Socket Client Connections
  31. Testing Network Application Functionality
  32. Extending Core Classes in Custom Modules
  33. Developing Unit Tests with Mocha
  34. Wrapping Up
  35. 4. Connecting Robust Microservices
  36. Installing ØMQ
  37. Publishing and Subscribing to Messages
  38. Responding to Requests
  39. Routing and Dealing Messages
  40. Clustering Node.js Processes
  41. Pushing and Pulling Messages
  42. Wrapping Up
  43. Node.js 8 the Right Way
  44. Part II. Working with Data
  45. 5. Transforming Data and Testing Continuously
  46. Procuring External Data
  47. Behavior-Driven Development with Mocha and Chai
  48. Extracting Data from XML with Cheerio
  49. Processing Data Files Sequentially
  50. Debugging Tests with Chrome DevTools
  51. Wrapping Up
  52. 6. Commanding Databases
  53. Introducing Elasticsearch
  54. Creating a Command-Line Program in Node.js with Commander
  55. Using request to Fetch JSON over HTTP
  56. Shaping JSON with jq
  57. Inserting Elasticsearch Documents in Bulk
  58. Implementing an Elasticsearch Query Command
  59. Wrapping Up
  60. Node.js 8 the Right Way
  61. Part III. Creating an Application from the Ground Up
  62. 7. Developing RESTful Web Services
  63. Advantages of Express
  64. Serving APIs with Express
  65. Writing Modular Express Services
  66. Keeping Services Running with nodemon
  67. Adding Search APIs
  68. Simplifying Code Flows with Promises
  69. Manipulating Documents RESTfully
  70. Emulating Synchronous Style with async and await
  71. Providing an Async Handler Function to Express
  72. Wrapping Up
  73. 8. Creating a Beautiful User Experience
  74. Getting Started with webpack
  75. Generating Your First webpack Bundle
  76. Sprucing Up Your UI with Bootstrap
  77. Bringing in Bootstrap JavaScript and jQuery
  78. Transpiling with TypeScript
  79. Templating HTML with Handlebars
  80. Implementing hashChange Navigation
  81. Listing Objects in a View
  82. Saving Data with a Form
  83. Wrapping Up
  84. 9. Fortifying Your Application
  85. Setting Up the Initial Project
  86. Managing User Sessions in Express
  87. Adding Authentication UI Elements
  88. Setting Up Passport
  89. Authenticating with Facebook, Twitter, and Google
  90. Composing an Express Router
  91. Bringing in the Book Bundle UI
  92. Serving in Production
  93. Wrapping Up
  94. Node.js 8 the Right Way
  95. 10. BONUS: Developing Flows with Node-RED
  96. Setting Up Node-RED
  97. Securing Node-RED
  98. Developing a Node-RED Flow
  99. Creating HTTP APIs with Node-RED
  100. Handling Errors in Node-RED Flows
  101. Wrapping Up
  102. A1. Setting Up Angular
  103. A2. Setting Up React
  104. Node.js 8 the Right Way

Emulating Synchronous Style with async and await

One of the most powerful new features in Node.js 8 is the introduction of async functions. Part of the 2017 ECMAScript draft specification, async functions allow you reap the benefits of Promises for simplifying code flow while structuring your code in a more natural way.

The key is that unlike a regular function, which always runs to completion, an async function can be intentionally suspended midexecution to wait on the resolution of a Promise. Note that this does not violate the central maxim that JavaScript is single-threaded. It’s not that some other code will preempt your async function, but rather that you choose to unblock the event loop to await a Promise.

An example should clarify. Consider this contrived function that returns a Promise.

​ ​const​ delay = (timeout = 0, success = ​true​) => {
​  ​const​ promise = ​new​ Promise((resolve, reject) => {
​  setTimeout(() => {
​  ​if​ (success) {
​  resolve(​`RESOLVED after ​${timeout}​ ms.`​);
​  } ​else​ {
​  reject(​`REJECTED after ​${timeout}​ ms.`​);
​  }
​  }, timeout);
​  });
​  ​return​ promise;
​ };

The delay function takes two arguments, a timeout in milliseconds and a success Boolean value that indicates whether the returned Promise should be resolved (true) or rejected (false) after the specified amount of time. Using the delay function is pretty straightforward—you call its .then() and .catch() methods to assign callback handlers. Here’s an example:

​ ​const​ useDelay = () => {
​  delay(500, ​true​)
​  .then(msg => console.log(msg)) ​// Logs "RESOLVED after 500 ms."​
​  .​catch​(err => console.log(err)); ​// Never called.​
​ };

The useDelay function invokes the delay to get a Promise that’s scheduled to be resolved after 500 milliseconds. Whether the Promise is resolved or rejected, the result is logged to the console.

Now, let’s see what useDelay would look like as an async function.

​ ​const​ useDelay = ​async​ () => {
​  ​try​ {
​  ​const​ msg = ​await​ delay(500, ​true​);
​  console.log(msg); ​// Logs "RESOLVED after 500 ms."​
​  } ​catch​ (err) {
​  console.log(err); ​// Never called.​
​  }
​ };

First, notice the addition of the async keyword in the function declaration. This signals that the function can use the await keyword to suspend while resolving a Promise.

Next, check out the await keyword inside the try{} block, right before the call to delay. Inside of an async function, await suspends execution until the Promise has been settled. If the Promise is resolved, then the await expression evaluates to the resolved value and the async function picks up where it left off.

On the other hand, if the Promise is rejected, then the rejection value gets thrown as an exception. In this case, we use the catch{} block to handle it.

Using async functions together with Promises presents a consistent, synchronous coding style for both synchronous and asynchronous operations. To practice, we’ll use async functions for the remaining bundle APIs that we’ll be adding.