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Learning Nodejs For Net Developers Harry Cummings
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- 6. Learning Node.js for.NET Developers
- 7. Table of Contents LearningNode.js for .NET Developers Credits About the Author About the Reviewer www.PacktPub.com eBooks, discount offers, and more Why subscribe? Preface What this book covers What you need for this book Who this book is for Conventions Reader feedback Customer support Downloading the example code Downloading the color images of this book Errata Piracy Questions 1. Why Node.js? What is Node.js? Understanding the Node.js execution model Non-blocking Event-driven Single-threaded Introducing the Node.js ecosystem Why JavaScript? A clear canvas Functional nature A bright future When to use Node.js Writing web applications Identifying other use cases Why now? Summary 2. Getting Started with Node.js Installing and running Node.js Choosing an editor Using an application framework Getting started with Express Exploring our Express application
- 8. Understanding Express routesand views Using nodemon for automatic restarts Creating modular applications with Express Bootstrapping an Express application Understanding Express middleware Implementing error handling Using Express middleware Summary 3. A JavaScript Primer Introducing JavaScript types JavaScript primitive types Functional object-oriented programming Functional programming in JavaScript Understanding scopes in JavaScript Strict mode Object-oriented programming in JavaScript Programming without classes Creating objects with the new keyword Programming with classes Class-based inheritance Summary 4. Introducing Node.js Modules Organizing your codebase JavaScript module systems Creating modules in Node.js Declaring a module with a name and its own scope Defining functionality provided by the module Importing a module into another script Defining a directory-level module Implementing an Express middleware module Summary 5. Creating Dynamic Websites Handling user-submitted data Communicating via Ajax Implementing other data operations Listing data in views Issuing a delete request from the client Splitting up Express views using partials Summary 6. Testing Node.js Applications Writing a simple test in Node.js Structuring the codebase for tests Writing BDD-style tests with Mocha Resetting state between tests
- 9. Using Chai forassertions Creating test doubles Creating test doubles using Sinon.JS Testing an Express application Simplifying tests using SuperAgent Full-stack testing with PhantomJS Summary 7. Setting up an Automated Build Setting up an integration server Setting up a public GitHub repository Building a project on Travis CI Automating the build process with Gulp Running tests using Gulp Checking code style with ESLint Automatically fixing issues in ESLint Running ESLint from Gulp Gathering code coverage statistics Running integration tests from Gulp Summary 8. Mastering Asynchronicity Using the callback pattern for asynchronous code Exposing the callback pattern Consuming asynchronous interfaces Writing cleaner asynchronous code using promises Implementing promise-based asynchronous code Consuming the promise pattern Parallelising operations using promises Combining asynchronous programming patterns Summary 9. Persisting Data Introducing MongoDB Why choose MongoDB? Object modeling JavaScript Scalability Getting started with MongoDB Using the MongoDB shell Using MongoDB with Express Persisting objects with Mongoose Isolating persistence code Dependency injection in Node.js Providing dependencies Running database integration tests on Travis CI Introducing Redis
- 10. Why use Redis? InstallingRedis Using Redis as a key-value store Storing structured data in Redis Building a user ranking system with Redis Using Redis from Node.js Testing with redis-js Implementing user rankings with Redis Making use of the users service A note on security Summary 10. Creating Real-time Web Apps Understanding options for real-time communication Introducing Socket.IO Implementing a chat room with Socket.IO Scaling real-time Node.js applications Using Redis as a backend Integrating Socket.IO with Express Directing Socket.IO messages Testing Socket.IO applications Organizing Socket.IO applications Exposing real-time updates to the model Organizing Socket.IO applications using namespaces Partitioning Socket.IO clients using rooms Summary 11. Deploying Node.js Applications Working with Heroku Setting up a Heroku account and tooling Running an application locally with Heroku Deploying an application to Heroku Working with Heroku logs, config, and services Setting up MongoDB Setting up Redis Deploying from Travis CI Setting encrypted Travis CI environment variables Installing Ruby Creating an encrypted environment variable Further resources Summary 12. Authentication in Node.js Introducing Passport Choosing an authentication strategy Understanding third-party authentication Using Express sessions
- 11. Specifying a sessionsecret Deciding when the session gets saved Using alternative session stores Using session middleware Implementing social login Setting up a Twitter application Configuring Passport Persisting user data with Redis Configuring Passport with persistence Hiding functionality from unauthenticated users Integration testing with Passport Allowing users to log out Adding other login providers Summary 13. Creating JavaScript Packages Writing universal modules Comparing Node.js and RequireJS Supporting the browser environment Using AMD modules with RequireJS Isomorphic JavaScript Writing npm packages Defining an npm package Publishing a package to npm Running automated clients on the web Releasing a standalone tool to npm Using Node.js modules in the browser Controlling Browserify's output Summary 14. Node.js and Beyond Understanding Node.js versioning A brief history of Node.js Introducing the Node.js LTS schedule Understanding ECMAScript versioning Exploring ECMAScript 2015 Understanding ES2015 modules Using syntax improvements from ES2015 The for... of loop The spread operator and rest parameters Destructuring assignment Introducing generators Introducing ECMAScript 2016 Going beyond JavaScript Exploring compile-to-JavaScript languages TypeScript
- 12. CoffeeScript And beyond... Introducing atrue assembly language for the web Understanding asm.js Understanding WebAssembly JavaScript and ASP.NET Exploring .NET Core Defining project structure in .NET Core Managing dependencies in .NET Core Building web applications in ASP.NET Core Integration with JavaScript Server-side JavaScript integration with .NET Summary Index
- 13. Learning Node.js for.NET Developers
- 14. Learning Node.js for.NET Developers Copyright © 2016 Packt Publishing All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior written permission of the publisher, except in the case of brief quotations embedded in critical articles or reviews. Every effort has been made in the preparation of this book to ensure the accuracy of the information presented. However, the information contained in this book is sold without warranty, either express or implied. Neither the author, nor Packt Publishing, and its dealers and distributors will be held liable for any damages caused or alleged to be caused directly or indirectly by this book. Packt Publishing has endeavored to provide trademark information about all of the companies and products mentioned in this book by the appropriate use of capitals. However, Packt Publishing cannot guarantee the accuracy of this information. First published: June 2016 Production reference: 1170616 Published by Packt Publishing Ltd. Livery Place 35 Livery Street Birmingham B3 2PB, UK. ISBN 978-1-78528-009-2 www.packtpub.com
- 15. Credits Author Harry Cummings Reviewer David Simons CommissioningEditor Kunal Parikh Acquisition Editor Rahul Nair Content Development Editor Trusha Shriyan Technical Editor Jayesh Sonawane Copy Editor Safis Editing Project Coordinator Kinjal Bari Proofreader Safis Editing Indexer Mariammal Chettiyar Graphics Disha Haria
- 16. Production Coordinator Nilesh Mohite CoverWork Nilesh Mohite
- 17. About the Author HarryCummings has been working in software development for 8 years, and for the past few years, he has performed the role of technical lead across a variety of projects for varied clients. He has, in the past, also worked as a developer, project manager, and consultant. This gives him an excellent all-round view of the role of a technical lead and its relationship with other roles as well as insight into every stage of project delivery, from initial analysis to long-term maintenance. Harry has extensive experience in C#/.NET, Java and Scala, and JavaScript/Node.js. He continues to work directly with these technologies on a regular basis in the teams that he leads. His broader interests and expertise lie in sharing and nurturing software development best practices through training and mentoring. He has appeared at conferences such as NDC London and SDD Conf, speaking about diverse topics, ranging from introductory Node.js through to automated test strategies and long-term project maintainability.
- 18. About the Reviewer DavidSimons is a London-based software consultant. He is familiar with a wide range of tools, having helped clients such as the BBC and News International deliver web solutions in a range of languages, including .NET, Java, and full-stack JavaScript. He shares his insights around these and his background in statistics research at a range of conferences, including NDC and JSConf. As of 2016, he works with London-based consultancy GraphAware to advocate and consult on the use of graph databases in modern applications.
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- 22. Preface The purpose ofthis book is to help .NET or Java developers make the leap to Node.js. You may have some web development experience, and perhaps you've written some browser-based JavaScript in the past. It might not be obvious why anyone would want to take JavaScript out of the browser and use it for server-side development. However, this is exactly what Node.js does. What's more, Node.js has been around for long enough now to have matured as a platform, and has sustained its impressive growth in popularity well beyond any period that could be attributed to initial hype over a new technology. The first objective of this book then is to explain why Node.js is a compelling technology that's worth learning more about. The first few chapters introduce Node.js with this in mind, quickly get you up and running with Node.js, and provide an important (re) introduction to the JavaScript language to set you on the right track. The main part of this book will then take you through a worked example of building up a Node.js web-application step by step. In the process, we'll illustrate all the important tools and techniques required for real-world development projects in Node.js. The aim is to make the most of your existing development expertise to allow you to quickly reach the same level of best practices and professionalism with Node.js. The final chapters of the book show how to use Node.js for other purposes outside of web applications and how to continue learning Node.js and exploring the ecosystem around it. We'll also see how you can use Node.js alongside .NET and benefit from applying your programming skills across both technologies.
- 23. What this bookcovers Chapter 1, Why Node.js?, introduces Node.js as a programming platform. It covers the execution model of Node.js, particularly how it differs from .NET and Java, and the use cases in which these differences become strengths. This chapter also discusses the suitability of JavaScript as a development language. Chapter 2, Getting Started with Node.js, dives straight into creating a Node.js application. In this chapter, you will install Node.js, choose a code editor, and set up a minimal web application project. You'll also learn some important command-line tools for working with Node.js. Chapter 3, A JavaScript Primer, introduces the most important things to know when programming in JavaScript. It describes the JavaScript type system and its particular flavor of functional object-oriented programming, including prototype-based inheritance. This chapter also covers a few key gotchas and JavaScript language quirks. Chapter 4, Introducing Node.js Modules, explains how to structure JavaScript applications using modules. It introduces the Node.js module system and shows you how to use this to organise your application's code. Chapter 5, Creating Dynamic Websites, expands on the examples from the previous chapter to build a functioning web application. You'll add a JSON API and dynamic views to your application and communicate between the client and server using Ajax. Chapter 6, Testing Node.js Applications, shows you how to write automated tests in JavaScript and Node.js. It introduces a number of tools and libraries for writing and running tests in JavaScript, and guides you through writing a variety of unit tests and integration tests for your application. Chapter 7, Setting up an Automated Build, covers build automation and continuous integration in Node.js. You'll set up a CI server and task runner for your application, adding automated tasks to run tests, execute static analysis, and assess code coverage. Chapter 8, Mastering Asynchronicity, introduces different patterns for asynchronous programming in JavaScript. You'll apply these to your own application and make the most of JavaScript language features and libraries for simplifying asynchronous code. Chapter 9, Persisting Data, explains persistent data stores that can be used with Node.js. It introduces MongoDB and Redis, explaining their different data models and their use cases. You'll integrate both of these data stores with your Node.js application. Chapter 10, Creating Real-time Web Apps, shows how to implement real-time two-way communication between the client and the server. You'll use the Socket.IO library to add real-time functionality into your application. You'll also see how to write tests for this functionality and
- 24. how to writescalable real-time applications using Redis as a backend. Chapter 11, Deploying Node.js Applications, demonstrates how to get a Node.js application onto the Web. You'll deploy your application to a free cloud-hosting provider. You'll see how to configure data stores and how to use remote server logs for debugging. Chapter 12, Authentication in Node.js, covers authentication for Node.js web applications. You'll implement authentication using third-party providers, integrate this with your application, and show different content to logged-in and logged-out users. Chapter 13, Creating JavaScript Packages, explains how to create standalone JavaScript packages for use by others. You'll see how to write universal JavaScript libraries that can run on both the client and the server, and how to write a standalone command-line application using Node.js. Chapter 14, Node.js and Beyond, puts the content of this book in a wider context. It explains how Node.js and JavaScript are continuing to evolve, so you can be prepared for and take advantage of upcoming changes. It covers some alternative programming languages for Node.js and the Web, and how these relate to JavaScript. It discusses how some of the principles from Node.js can be applied to .NET programming, and illustrates how these are particularly visible in .NET Core (the new version of .NET). It also shows how you can use Node.js together with .NET to gain the best of both worlds.
- 25. What you needfor this book All of the tools and services used in this book are available for free online. Most of the worked examples require an active web connection at some point. To get started, you need nothing more than a console, a web browser, and permission to install new software on your machine. To support developers coming from a .NET background, some of the console listings or example steps in this book use Windows conventions (for example, backslashes in paths). None of the examples depend on Windows specifically though. You can work through this book on Windows, Mac OSX, or Linux.
- 26. Who this bookis for This book is for .NET or Java developers who are interested in learning Node.js. No prior experience with Node.js is expected. You might have written some client-side JavaScript before, but this is not required. The main worked example in this book is a Node.js web application. Web development experience in .NET or Java will be helpful, but it's not necessary to have experience with any particular application library or framework.
- 27. Conventions In this book,you will find a number of text styles that distinguish between different kinds of information. Here are some examples of these styles and an explanation of their meaning. Code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles are shown as follows: "ES2015 introduces the let keyword for declaring variables." A block of code is set as follows: <!DOCTYPE html> <html> <head> <title>{{ title }}</title> <link rel='stylesheet' href='/stylesheets/style.css' /> </head> <body> <h1>{{ title }}</h1> <p>Welcome to {{ title }}</p> </body> </html> When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold: /* GET home page. */ router.get('/', function(req, res, next) { res.render('index', { title: 'Express', name: 'World' }); }); Any command-line input or output is written as follows: > npm install –g nodemon New terms and important words are shown in bold. Words that you see on the screen, for example, in menus or dialog boxes, appear in the text like this: "Clicking the Next button moves you to the next screen." Note Warnings or important notes appear in a box like this. Tip Tips and tricks appear like this.
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- 35. Chapter 1. WhyNode.js? Node.js is still relatively new compared to platforms such as .NET and Java, but has become very popular in a short time, and has even started influencing these platforms. This is thanks to its distinctive programming model, extensive ecosystem, and powerful tooling. These factors make Node.js a compelling alternative to other platforms. They can also make it intimidating. Its distinctive programming model may seem quite alien compared to other platforms. The sheer range of available libraries and tools can be bewildering. This book will guide you through Node.js so you can start using it in your applications. It will help you to understand Node.js, navigate its ecosystem, and leverage your existing development skills in this new environment. In this chapter, we will cover the following topics: Introducing the Node.js platform Seeing how its execution model works Exploring the Node.js ecosystem Looking at JavaScript as a language choice Considering the range of use cases for Node.js
- 36. What is Node.js? Node.jsconsists of a JavaScript engine together with low-level APIs for core server-side functionality. The execution engine is the same V8 engine developed for the Chrome web browser. Node.js takes this engine and embeds it in a standalone application that can run JavaScript outside the browser. In Node.js, the standard APIs found in browsers to support client-side web development, such as the Document Object Model (DOM) and XMLHttpRequest, are not present. Instead, there are APIs to support general-purpose application development. These core APIs cover low-level functionality such as the following: Networking and security Accessing the file system Defining and requiring modules Raising and consuming events Handling binary data streams Compression UTF-8 support Retrieving basic information about the OS Managing child processes Some of these APIs may already be familiar from developing client-side JavaScript. For example, the Timers API exposes the familiar setTimeout and setInterval functions. Node.js also provides several tools to help with the development process. These include console logging, debugging, a Read-Eval-Print Loop (REPL) (or interactive console), and basic assertions for testing.
- 37. Understanding the Node.jsexecution model The execution model of Node.js follows that of JavaScript in the browser. It is quite different from that of most general-purpose programming platforms. Stated formally, Node.js has a single-threaded, non-blocking, event-driven execution model. We will define each of these terms in this section. Non-blocking Put simply, Node.js recognizes that many programmes spend most of their time waiting for other things to happen, for example, slow I/O operations such as disk access and network requests. Node.js addresses this by making these operations non-blocking. This means that program execution can continue while they happen. For example, the filesystem API's stat function for retrieving statistics about a file may be called as follows: fs.stat('/hello/world', function (error, stats) { console.log('File last updated at: ' + stats.mtime); }); Two arguments are passed to the fs.stat function: the name of the file that we are interested in, and a callback function. The fs.stat call returns immediately, returning control of execution to the current thread but not returning a value. If there are further commands following the fs.stat call, these will then be executed. Otherwise, the thread is released to perform other work. The callback function is invoked (that is 'called back') only after the runtime has finished communicating with the filesystem. The result of the filesystem operation is passed into the callback function. This non-blocking approach is also called asynchronous programming. Other platforms support this (for example, C#'s async/await keywords and .NET's Task Parallel Library). However, it is baked in to Node.js in a way that makes it simple and natural to use. Asynchronous API methods are all called in the same way as fs.stat. They all take a callback function that gets passed error and result arguments. Event-driven The event-driven nature of Node.js describes how operations are scheduled. In typical procedural environments, a program has an entry point that executes a set of commands until completion, or enters a loop and performs some processing on each iteration. Node.js has a built-in event loop, which isn't exposed to the developer. It is the job of the event loop to decide which piece of code to execute next. Typically, this will be a callback function that is ready to run in response to some other event. For example, a filesystem operation may have completed, a timeout may have expired, or a new network request may have arrived. This built-in event loop simplifies asynchronous programming by providing a consistent approach
- 38. and avoiding theneed for applications to manage their own scheduling. Single-threaded The single-threaded nature of Node.js simply means that there is only one thread of execution in each process. Also, each piece of code is guaranteed to run to completion without being interrupted by other operations. This greatly simplifies development and makes programs easier to reason about. It removes the possibility for a range of concurrency issues. For example, it is not necessary to synchronize/lock access to shared in-process state as it is in Java or .NET. A process can't deadlock itself or create race conditions within its own code. Single-threaded programming is only feasible if the thread never gets blocked waiting for long-running work to complete. Thus, this simplified programming model is made possible by the non-blocking nature of Node.js.
- 39. Introducing the Node.jsecosystem The built-in Node.js APIs provide a low-level core for creating applications. Applications typically only use a small number of these APIs directly. They often use third-party library modules that provide higher-level abstractions for application development. Node.js has its own package manager, npm. This is similar to .NET's NuGet or the package management aspects of Java's Maven. Applications specify their dependencies in a simple JSON file. The npm registry provides a central repository for packages. This registry has grown rapidly and is already much larger (in terms of number of available packages) than the corresponding repositories for other platforms (see http://www.modulecounts.com/). There are hundreds of thousands of packages available, providing a vast array of functionality. The npm command line tool can be used to download packages and install new ones. Library dependencies are installed locally to each application. Some packages provide command-line tools, which may be installed globally rather than under a specific project. Many frameworks available on npm are split into a small extensible core and a number of composable modules. This approach makes it easy to understand the libraries on which your application depends, avoiding the need to reason about complex heavyweight frameworks. The consistency of calling non-blocking (asynchronous) API methods in Node.js carries through to its third-party libraries. This consistency makes it easy to build applications that are asynchronous throughout.
- 40. Why JavaScript? JavaScript isa language that can seem unintuitive compared to other popular object-oriented (OO) languages. It also has a number of quirks and flaws that have drawn criticism (and occasional ridicule). It might then seem a surprising choice of language for a new programming platform. This section discusses the factors that make JavaScript a more appealing choice.
- 41. A clear canvas Thesize and complexity of JavaScript is part of its appeal. The core language itself, which doesn't include APIs such as the DOM, is small and simple. This makes it easy for Node.js to establish its own styles and conventions. The new APIs provided by Node.js and the consistent approach to asynchronous programming wouldn't be possible in a more complex language with a larger pre-existing standard class library.
- 42. Functional nature JavaScript wasfirst built as a programming language for client-side functionality in the browser. This might not make it an obvious choice for general-purpose programming. In fact, these two use cases do have something important in common. User interface code is naturally event-driven (for example, binding event handlers to button clicks). Node.js makes this a virtue by applying an event-driven approach to general-purpose programming. JavaScript supports functions as first-class objects. This means it's easy to create functions dynamically and pass around references to them. This fits in well with the asynchronous, non- blocking approach of Node.js. In particular, it's easy to expose and use APIs based around callback functions.
- 43. A bright future JavaScripthas received a lot of attention in the last several years as it has become more widely used for providing rich functionality on the Web. Browser vendors have put a huge amount of engineering effort into improving the performance of JavaScript. Node.js benefits from this directly via its use of Chrome's V8 engine. The JavaScript language itself is undergoing some major changes for the better. The ECMAScript 2015 standard (previously known as ES6) represents the most significant revision of the language in its history. It introduces features that make the language more intuitive and less verbose. It also addresses flaws that JavaScript has been criticized for in the past, removing gotchas and making programs easier to reason about.
- 44. When to useNode.js As discussed earlier in this chapter, Node.js recognizes that I/O is a bottleneck for many applications. On most programming platforms, threads will waste time blocking on I/O operations. There are approaches developers can take to avoid this, but these all involve adding some complexity to their code. In Node.js, the platform itself provides a completely natural approach.
- 45. Writing web applications Theflagship use case for Node.js is building web applications. These are inherently event-driven as most or all processing takes place in response to HTTP requests. Also, many websites do little computational heavy-lifting of their own. They tend to perform a lot of I/O operations: Streaming requests from the client Talking to a database, locally or over the network Pulling in data from remote APIs over the network Reading files from disk to send back to the client These factors make I/O operations a likely bottleneck for web applications. The non-blocking programming model of Node.js allows web applications to make the most of a single thread. As soon as any of these I/O operations starts, the thread is immediately free to pick up and start processing another request. Processing of each request continues via asynchronous callbacks when I/O operations complete. The processing thread is only kicking off and linking together these operations, never waiting for them to complete. This allows Node.js to handle a much higher rate of requests per thread than other platforms. You can also still make use of multiple threads (for example, on multi-core CPUs) by simply running multiple instances of the Node.js process.
- 46. Identifying other usecases There are of course some applications that don't perform much I/O and are more likely to be CPU bound. Node.js would be less suitable for computationally-intensive applications. Programs that do a lot of processing of in-memory data are less concerned about I/O. Web applications are not the only I/O-heavy applications though. Other classes of program that could be a good candidate for Node.js include the following: Tools that manipulate large amounts of data on disk Supervisor programs coordinating other software or hardware Non-browser GUI applications that need to respond to user input Node.js is especially suitable for glue applications that pull together functionality from other remote services. The increasing popularity of microservices as an architectural pattern makes this kind of application more common.
- 47. Why now? Node.js hasbeen around for several years, but now is the perfect time to start using it if you haven't already. The release of Node.js v4 towards the end of 2015 consolidated the project's governance model and heralds Node.js coming to maturity. It also allows the project to keep more up to date with the V8 engine. This means that Node.js can benefit more directly from ongoing development on V8. For example, security and performance improvements to V8 will now make their way into Node.js much sooner. As discussed earlier in this chapter, the release of the ECMAScript 2015 standard makes JavaScript a much more appealing language. It pulls in useful features from other popular OO languages and resolves a number of long-standing flaws in JavaScript. Meanwhile, the ecosystem of third party libraries and tools around Node.js and JavaScript continues to grow. Node.js is treated as a first-class citizen by major hosting platforms. Companies such as Google and Microsoft are also throwing their weight behind JavaScript and related technologies.
- 48. Summary In this chapter,we have understood Node.js and its distinctive execution model, explored the growing ecosystem around Node.js and JavaScript, seen the reasons for JavaScript as a language choice, and described the kinds of application that can benefit from Node.js. Now that you know how Node.js works and when to use it, it's time to dive in and get our first Node.js application up and running.
- 49. Chapter 2. GettingStarted with Node.js This chapter will get you up and running with Node.js. You'll see how quick this can be and how easy it is to start writing web applications. You'll also choose a development environment for working with Node.js. In this chapter, we will cover the following topics: Installing Node.js Writing our first Node.js web application Setting up our development environment
- 50. Installing and runningNode.js To install Node.js, visit https://nodejs.org, and download and run the installer package for the currently recommended version. The examples in this book are based on Node.js v6, released in April 2016 and supported through to April 2018. After installation, open up a console window (run command prompt on Windows, or terminal on Mac) and type node. This opens the Node.js REPL, which works like the JavaScript console in browsers. Try typing in a few commands and see the output: > function square(x) { return x*x; } undefined > square(42) 1764 > new Date() 2016-05-02T16:08:41.915Z > var foo = { bar: 'baz' } undefined > typeof foo 'object' > foo.bar 'baz' Now let's make use of one of the Node.js-specific APIs to create an HTTP server. Type the following commands into the REPL(the output of each command is omitted from the listing below for brevity): > var listener = function(request, response) { response.end('Hello World!') } > require('http').createServer(listener).listen(3000) Now try visiting http://localhost:3000 in your browser. Congratulations! You have written your first web server, in just two lines of code. The first line defines a callback function for handling HTTP requests and returning a response. The second line sets up a new server that accepts HTTP requests on port 3000 and invokes our callback function for each request. You can exit the Node.js REPLby typing process.exit().
- 51. Choosing an editor Ofcourse, we're not going to write all of our code inside the REPL. You can use any text editor or IDE you like for writing JavaScript for Node.js. If you're not sure what to use, try one of the following: Atom (https://atom.io/) Visual Studio Code (https://code.visualstudio.com/) These are both free, lightweight IDEs that are actually implemented in Node.js. They are both available for Windows, Mac, and Linux. The code listings in the rest of this book will be JavaScript source code files, not commands to be typed into the REPL.
- 52. Using an applicationframework The server we created in the REPLused the low-level HTTP module built into Node.js. This provides an API for creating a server that reads data from requests and writes to responses. As with other programming platforms, there are frameworks available providing more useful high-level abstractions for writing web applications. These include things such as URLrouting and templating engines. ASP.NET MVC, Ruby on Rails, and Spring MVC are all examples of such frameworks on different platforms. Note Example code If you get stuck at any point in this book, you can follow along with the code at https://github.com/NodeJsForDevelopers (there is a repository for each chapter and a commit for each heading that introduces any new code). In this book, we'll be using a framework called Express to write a web application in Node.js. Express is the most popular web application framework for Node.js. It is well suited to small- scale applications such as the one we'll be building. It also provides a good introduction to important concepts. Most other popular Node.js web application frameworks are conceptually similar to Express, and several are actually built on top of it.
- 53. Getting started withExpress To get our Express-based application started, we'll use npm to install the express-generator package, which will create a skeleton application based on Express. Run the following command in the console (that is, your regular terminal, not inside the Node.js REPL): > npm install -g express-generator@~4.x The -g option installs the Express generator globally, so you can run it from anywhere. The next command we run will create a new folder to contain our application code, so run this command wherever you want this folder to reside: > express --hogan chapter02 Note Templating engines Express offers a choice of templating engines. We'll be using Hogan, which is an implementation of the Mustache templating engine. You may already be familiar with Mustache from client-side libraries. Don't worry if not, though. It's very simple to pick up. As you can see from the output, this sets up a minimal standard application structure for us. Now run the following command (as instructed by the generator output) to install the modules on which our application depends: > cd chapter02 > npm install The generator has created a skeleton Node.js web application for us. Let's try running this: > npm start Now visit http://localhost:3000 again and you'll see the Express welcome page as shown here:
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- 56. There was alittle of everything in his “Ah!” A man falling from a balloon must utter such an “Ah!” when he crashes against the ground. Meanwhile, twice the cheers burst forth. Hymns of welcome were intoned, for silence had been kept till then. The duke had appeared to be addressing himself to both the young girls. The people did not know exactly which one might be the duchess; but their enthusiasm knew no bounds all the same. A great eddy pushed the crowd in a mass along the way to the castle, amid the blare of trumpets and rattling of rifle-shots. The voivodes formed the archway of steel above the heads of the duke and Helia, followed by Ethel. Endless cheering saluted them: “Long live the duke! Long live the duchess! Long live Morgana!” “Well!” thought Caracal, “this is getting to be amusing. I had thought all my chances lost, but they are coming back. Miss Ethel is still free! Helia a duchess! Well, stranger things have been seen; but all the same it is funny. After my ‘House of Glass’ and ‘Worms from a Dung-hill’ I shall study from nature a ducal marriage and make it a roman à clef! I shall write up every class of society—bourgeois, peasants, and princes! He certainly will marry her: you can’t trifle with an oath among such a population of fools; there are currents you can’t stem.” And so Caracal shouted louder than the others: “Long live Morgana! Long live the duchess!” Then he offered his arm to Miss Rowrer, who refused it! “What are they crying ‘Long live the duchess!’ for?” she asked Caracal, as they issued from beneath the steel arch, surrounded by children who wafted kisses toward them and bombarded them with flowers. Caracal recounted the oath which had been taken in
- 57. presence of thepeople, and before God. The duke had sworn to offer the heroine his titles and his throne. “Poor duke!” thought Ethel; “he really believed it was I— otherwise he would have sworn to nothing. Well, let it be so! We shall see if an oath is a sacred thing, or if women are only dolls for amusement. We shall see if the duke is a man!” Ethel now knew the whole story. On the yacht, that very evening, she had chanced to hear Helia talking with Suzanne. Their few words had been a revelation to her. She had already imagined what now she knew. The cow painting in the Luxembourg, the whole little combination invented by Caracal, all the coarse horse-play—ah! if Phil thought she was going to think less of him because of it, how mistaken he was! All that was about as important to her as Mr. Charley’s hair, brushed like a horse’s mane, and his velvet trousers— less than nothing at all! But Phil had other reasons to blush for himself, indeed. She understood his embarrassed air when he spoke of Helia. That he should promise marriage with an oath, should give hopes of happiness to Helia and lift her above her position, and then thrust her back into her hard life—that Phil, a Christian and an American, should do a thing like that! Ethel also knew the duke’s love-making to Helia. Poor Helia! simply a plaything for those two men!
- 58. “The duke stoodalone” She looked with admiration at the splendid couple before her,— the duke and Helia,—without a glance at the two men beside her— Phil and Caracal. Helia was superb. The red lights, shaken by the wind, illuminated her. The popular enthusiasm was beyond description; the crowd pressed forward behind the torch-bearers along the way. They touched her garments like the relics of a saint. The women lifted up
- 59. their children tomake them see Morgana. Young girls sang in chorus, while young men twirled their sabers aloft in warlike rhythm. All at once, above the crowd, far away in the mountains flames arose; the bonfires blazed up on each side of the bay and over the cliffs. An immense blaze, like a giant torch, threw great shadows and blinding streaks of light over the city. Its glow appeared through the night, leaping over space from peak to peak, to the far horizon, where it mingled with the stars. Helia and Ethel were amazed at the grandeur of the sight, and at the loving ardor of the crowd, in whose eyes, too, the flame seemed burning. Their own beauty struck everybody; surely the new duchess would be the most popular that Morgania had ever known, to judge from the delirious enthusiasm let loose by her presence. “What has taken hold of them?” thought Helia. “One might say I had done something extraordinary.” Helia for a moment was separated from Ethel. Beyond them the way, lonely and bare, mounted up to the castle. Guards watched over the approach. High above them the stained-glass window of Morgana reflected glitteringly the torches and bonfires. In a few steps more Helia, on the duke’s arm, would leave the people behind her and mount up, followed by the nobles, to the Hall of Ancestors. But just then there was a great rush forward, and as Helia, in real fright at this wild enthusiasm, pressed against the duke, she felt a sharp pain between her shoulders. She gave a little cry, and struggled toward the open space before her; but her breath failed and she fell. “Oh, the coward!” she murmured. “He would never have dared strike me to my face!”
- 60. “What is thematter?” the duke said, grasping her in his arms, “you are bleeding!” “Oh! what has happened?” asked Ethel, who came up at this moment, followed by Suzanne. “Helia! what has happened to you?” “He has killed me!” said Helia. “It is he who has done it!” cried Suzanne, with a terrible look, searching for some one in the crowd. “He—who?” “Socrate!” It was indeed Socrate. But he was no longer there. He had already disappeared into the shadow, seized by avenging hands, mangled by a people’s fury, trampled under foot into blood and mud! Helia had guessed rightly. Socrate had come on board the Columbia at Marseilles, where they had hastily taken on firemen. Under the exasperation of want, he took this occasion to follow Helia. He had learned as he prowled around the circus that she was going to Morgania on Miss Rowrer’s yacht, and he was not the man to let go his prey. The events of the last day above all else had stirred him to fury. Helia a duchess! Helia in grandeur, while he, the misunderstood genius, should drag out his life in an attic! Ah! you will not be mine? Then you shall be no one’s! He had seized the occasion and planted his knife between Helia’s shoulders. “Helia!” sobbed Suzanne. “Do you hear me? Answer!” But Helia did not. The duke and Phil, terrified, bore her to the throne-room. The torches cast a tragic light upon the group. Immense shadows lengthened themselves out before them. The
- 61. duke and Phil,bearing Helia, slowly advanced. The hall opened high before them, lighted dimly.
- 62. CHAPTER X “ON YOURKNEES!” They laid Helia down at the foot of Phil’s picture, on the great ancestral throne on which the duke had hoped to seat himself beside Miss Rowrer. The iron candelabrum, hanging from the arch, lighted the hall. But Morgana’s stained window, more than all the rest, blazed with sanguinary flashes. This time it was not the sunset, as the duke had described it to Miss Rowrer, when he showed her the engraving in Paris; it was the light of torches and of the giant bonfire shining through it from without. The heroic statues, Thilda, Rhodaïs the Slave, and Bertha the Horsewoman, seemed to live again beneath the glow. The flashes of light from the window seemed to make them palpitate. One would have said that joy swelled their marble breasts when Helia, whose bodice had been undone, and whose wounds were bandaged, opened her eyes and breathed freely as she asked: “Where am I?” “Oh, what a fright you’ve given us!” said Suzanne; “but now you’re saved. Do you suffer?” Helia was not suffering. To die was nothing,—but to fall, struck from behind by such a man! “If you had been there, Phil,” Helia said, speaking low, “you would have protected me, would you not? Oh, with you I should fear nothing. Give me your hand and stay with me!” Phil, with downcast eyes full of tears, took her hand.
- 63. “Look me inthe face; why do you lower your eyes, Phil?” she said, so that he alone could hear her. She added, with an indescribable regret in her voice: “Have I ever reproached you? Look me in the face, as in the old days! I wish you to be happy. I do not wish you to be sad!” From the city came a confused murmur, like the noise of the sea; and then there were long moments of silence. The nobles had not dared to enter the hall. The people’s deep anxiety was making itself felt. Suzanne, meanwhile, was arranging the cushions under Helia’s head. The duke had gone a little away. “Yes,” he was saying to himself, “Miss Rowrer will understand the sacrifice I am making for her. I fail in my word, it is true, but she will be grateful to me for not having made Helia her rival. As to the people, Miss Rowrer’s millions will make them forget my perjury.” Ethel, with Caracal at her elbow, gave to a servant the basin of water and bloody cloths. Impassive as the marble ancestresses, she turned her clear eyes on Phil and the duke. “Phil,” Helia continued, as she pressed his hand, “you promised me once—do you remember?—when you loved me, in the old days? I understand, many things have passed since; and you are no longer the same man. Come here, Phil, nearer, nearer! I want to tell a secret in your ear. I have loved only you, Phil; every day I have waited for you, and you never came! I was mad, I know; it was impossible! But when one is young one is ignorant—and I believed you! Now you love another. Phil, I forgive you; but leave your hand in mine.” Phil was silent and red with shame. Ah, indeed, he remembered! Helia felt his heart beating in the hand which pressed her own. An intense emotion overpowered him. He had the fearful calm which goes before a storm. Neither the duke nor Phil spoke, motionless, by
- 64. the side ofHelia, who was resting tranquilly, while they made a room ready for her. “You can get up and go to it by yourself,” said Suzanne. “You’re safe. You haven’t lost much blood—Socrate’s blow missed!” “What!” murmured Ethel. “Our heroic Helia is going to die in the presence of these two men who loved her, without one of them asking her pardon for their false oaths?” “They accuse me of being cynical, but I should be more loyal than that,” said Caracal, with his gaze fixed on Ethel. “Look at your work, M. Caracal,” Ethel replied, in a low tone of contempt. “Those two men are your pupils. The duke, who will not see that the fortune of nations is courage and respect for promises— and Phil, whom I thought more noble,—look at him, blushing with shame, lowering his eyes,—these are the men according to your heart! They are the men who consider woman a plaything, and abandon her when she ceases to please! I forgive you your Richard the Lion-hearted, your blackmailing, and your infamies, but look at the result of your bad example and ignoble theories! When you threw Helia at Socrate that you might study passion cheaply, without knowing it you put the dagger in the assassin’s hand. Helia struck down from behind,—it is your work! The duke, forgetful of duty and aiming at Helia for his mistress, it is your work! Phil, with his false promises, is worthy of you! Two men spoiled, one assassin, and a dying woman—look at your work, M. Caracal!” The “subtle observer,” a poor human rag blown down by a breath, collapsed into a chair. The great window still threw its burning glow upon the throne. The marble ancestors, dimly lighted, seemed to lift their heads to curse the feeble duke. They formed a circle round the hall and the
- 65. throne where Heliawas resting—Helia, brave as Rhodaïs, intrepid as Thilda, invulnerable as Bertha—Helia, the Morgana announced and foretold. The duke was pale and grave. He looked at Helia, and then turned his head toward Ethel. All at once Ethel saw Helia rise upon her elbow, with one hand convulsively grasping that of Phil, and the other signing to listen. Through the half-open door floated a far-away melody, so weak, so far away—Phil felt its thrill in his heart. Le roi fait battre le tambour Pour appeler ses dames, Et la première qu’il a vue Lui a ravi son âme. The king had the drum beat To call out his ladies— And the first one he sees Steals away his soul. It seemed to come with the sea-breeze from beyond the murmurs of the land. It was the music of the yacht playing the air chosen by Ethel, that air which Helia hummed when she was alone. Ethel had foreseen the hour when Helia would be entering the throne-room. The music from the yacht was to greet her triumph. Now it seemed to be soothing her agony. “Listen, Phil, listen!” said Helia; “do you remember?” Phil remembered all and saw all once more—his first love, the little Saint John, the Louvre paradise, all his promises! His youth blossomed in his heart.
- 66. In his breastrose a flame which burned away every selfish thought. Yes, he had promised! Helia had lived in that only hope; he had let her fall from the height of her dream! He had shut off the future from her. He had dug a pit with his selfishness, and pushed Helia into it when she ceased to please! He had turned his back on her despair! It seemed to him that a giant hand was bending him low before Helia and a voice was saying: “Down on your knees!” Quickly, quickly and low, as one might confess a crime, Phil spoke: “Yes, I was wrong—yes, I promised. I ask pardon, Helia! How I shall thank God if he will let you live, that I may blot out my fault!” “Oh, Phil!” murmured Helia. “I love you still,” said Phil; “and you shall be my wife. You will see how happy we shall be—Helia, forgive me!”
- 67. “‘My people awaittheir duchess’” “Let me kiss your lips!” said Helia. Ethel had drawn near, followed by Caracal. There was a strange light in her eyes. “See,” she said to Caracal. “Glory to those who are struck down by the light like St. Paul. There is joy in heaven for the repenting sinner!” “Will you ever pardon me?” stammered Caracal.
- 68. “Perhaps; tears washaway many things,” added Ethel, remembering how Phil had already pardoned Caracal because he had seen him weeping. “That is a man worth loving, a rare thing,” Ethel thought as she looked at Phil. Helia now was sitting up; the wound no longer bled. “How happy I am!” said Helia. She wept with joy. Phil was at her knees as in the old days. “Listen,” she said, “it is our tune of the old times, Phil! I seem still to be there!” Phil kissed her hands to hide his tears. “Phil,” said Helia, with a timid look at Ethel, and in a tone so low that it could come only from the heart, “tell me, Phil, am I really fit to be your wife?” The door opened slowly, a bright light burst into the hall. It was the voivodes coming for information. If a misfortune had happened to one of the maidens, perhaps to their duchess, when they were on the spot, sword in hand to form a sheltering arch above her—what a shame it would be for them! If the duchess was dying, they would pray for her on their knees. They approached in silence. The duke had drawn near Ethel. “I love you!” he said, speaking low. “See what I have done for you! I swore—but I thought it was you. There is still time. My people await their duchess. Shall it be you, Miss Rowrer?” The duke held out his hand in an attitude of deepest respect. Miss Rowrer stopped him short with a gesture. She had judged the two men. This ruler who would not keep his oath, sworn in the name of his ancestors—he should never be husband of hers. To her titles were nothing, character was all. Calm as Justice, with her eyes
- 69. fixed straight onthe duke, she pointed with her hand to Phil, kneeling beside Helia, and said: “That is a Man!”
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