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The Node Craftsman Book

You're reading from   The Node Craftsman Book An Advanced Node.js Tutorial

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Product type Paperback
Published in Apr 2017
Publisher Packt
ISBN-13 9781787128149
Length 186 pages
Edition 1st Edition
Languages
Tools
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Author (1):
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Manuel Kiessling Manuel Kiessling
Author Profile Icon Manuel Kiessling
Manuel Kiessling
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Toc

Table of Contents (17) Chapters Close

Preface 1. Part 1: Node.js Basics in Detail FREE CHAPTER 2. Working with NPM and Packages
3. Test-driven Node.js Development
4. Object-oriented JavaScript 5. Synchronous and Asynchronous Operations Explained 6. Using and Creating Event Emitters 7. Optimizing Code Performance and Control Flow Management Using the Async Library 8. Node.js and MySQL 9. Node.js and MongoDB 10. Part 2: Building a Complete Web Application with Node.js and Angular 11. Milestone 1 – A First Passing Test Against the Server
12. Milestone 2 – The API Responds with Actual Database Content 13. Milestone 3 – Setting the Stage for a Continuous Delivery Workflow 14. Milestone 4 – Giving Users a Frontend 15. Milestone 5 – More Work on the Backend 16. Milestone 6 – Completing the Backend and Finalizing the Application

Creating your own event emitter object

We can create event emitters ourselves. This is even supported by Node.js by inheriting from the built-in events.EventEmitter class. But let's first implement a simple event emitter from scratch, because this explains the pattern in all its details.

For this, we are going to create a module whose purpose is to regularly watch for changes in the size of a file. Once implemented, it can be used like this:

'use strict';

watcher = new FilesizeWatcher('/path/to/file');

watcher.on('error', function(err) {
  console.log('Error watching file:', err);
});

watcher.on('grew', function(gain) {
  console.log('File grew by', gain, 'bytes');
});

watcher.on('shrank', function(loss) {
  console.log('File shrank by', loss, 'bytes');
});

watcher.stop();

As you can see, the module consists...

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