《Node.js实战指南》：快速掌握服务器端JavaScript开发

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"《Node.js：正确的方式》是一本专为Jabezzhang准备的前端开发指南，旨在帮助读者快速入门并深入了解现代服务器端JavaScript编程。作者们如Allen Wirfs-Brock（ECMAScript语言规范项目编辑）推崇它为初学者提供了全面且深入的学习资源，强调这本书是学习Node.js的首选教材。书中超越了基础的JavaScript和Node.js概念，深入探讨了构建高质量服务器应用程序的实质内容。Rick Waldron（Bocoup, LLC的软件工程师）指出，这不仅仅是一本介绍Node.js作为 hipster 风格Web应用服务器的书籍，而是展现了其灵活性和强大功能，适合任何希望探索服务器基础设施的JavaScript开发者。 Eric Redmond（《七个星期七种数据库》合著者）认可《Node.js：正确的方式》是一本实用性强、内容丰富的读物，它跳过了简单的示例，而是通过实际案例演示Node.js的应用潜力，让读者能够快速领略其在服务器世界中的作用。最后，来自Baydin, Inc.的Xavi Ramirez也高度评价此书，认为它是学习Node.js的最佳选择，书中直接引入了与实际项目相关的示例，帮助读者跨越“Hello World”阶段，步入更有深度的开发领域。《Node.js：正确的方式》不仅提供了基础知识，还为开发者提供了丰富的实践经验，是踏上Node.js编程之旅的理想起点，无论你是新手还是寻求提升的开发者，都能从中受益匪浅。"

East of the mountain range, we find the client-side programs. These include

GUI tools of all stripes, consumer applications, mobile apps, and web apps.

Client-side programs interact directly with human beings, often by waiting

patiently for their input.

West of the mountains are the server-side programs. This vast expanse is

Node.js territory.

Deep within the server-side region lies the Web—that old guard of HTTP, Ajax,

REST, and JSON. The websites, apps, and APIs that consume so much of

our collective mental energy live here.

Because we spend so much time thinking about the Web, we overemphasize

Node’s use in developing web applications. People ask, “How is Node better

for making web apps?” or, “How can I make a REST service with Node?”

These are good questions, but they miss the point. Node is great for a wider

range of things, and this book explores that larger world.

Node’s Niche

Since JavaScript’s first appearance in 1995, it has been solving problems all

along the front-end/back-end spectrum. The following figure shows this

spectrum and where Node.js fits within it.

Figure 2—Node’s place in the JavaScript spectrum

In the web browser on the right, much of the scripting involves waiting for

user interaction. Click here, drag that, choose a file, etc. JavaScript has been

extraordinarily successful in this space.

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As long as there’s something left to do, Node’s event loop will keep spinning.

Whenever an event occurs, Node invokes any callbacks (event handlers) that

are listening for that event.

As a Node developer, your job is to create the callback functions that get

executed in response to events. Any number of callbacks can respond to any

event, but only one callback function will ever be executing at any time.

Everything else your program might do—like waiting for data from a file or

an incoming HTTP request—is handled by Node, in parallel, behind the scenes.

Your application code will never be executed at the same time as anything

else. It will always have the full attention of Node’s JavaScript engine while

it’s running.

Single-Threaded and Highly Parallel

Other systems try to gain parallelism by running lots of code at the same

time, typically by spawning many threads. But not Node.js. For JavaScript,

Node is a single-threaded environment. At most, only one line of your code

will ever be executing at any time.

Node gets away with this by doing most I/O tasks using nonblocking

techniques. Rather than waiting line-by-line for an operation to finish, you

create a callback function that will be invoked when the operation eventually

succeeds or fails.

Your code should do what it needs to do, then quickly hand control back over

to the event loop so Node can work on something else. We’ll develop practical

examples of this throughout the book, starting in Chapter 2, Wrangling the

File System, on page 9.

If it seems strange to you that Node achieves parallelism by running only one

piece of code at a time, that’s because it is. It’s an example of something I call

a backwardism.

Backwardisms in Node.js

A backwardism is a concept that’s so bizarre that at first it seems completely

backwards. You’ve probably experienced many backwardisms while learning

to program, whether you noticed them or not.

Take the concept of a variable. In algebra it’s common to see equations like

“

7x + 3 = 24

.” Here,

is called a variable; it has exactly one value, and your job

is to figure out what that value is.

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Then when you start learning how to program, you quickly run into statements

like “

x = x + 7

.” Now

is still called a variable, but it can have any value that

you assign to it. It can even have different values at different times.

From algebra’s perspective, this is a backwardism. The equation “

x = x + 7

”

makes no sense at all. The notion of a variable in programming is not just a

little different—it’s 100 percent backwards. But once you understand the

concept of assignment, the programming variable makes perfect sense.

So it is with Node’s single-threaded event loop. From a multithreaded perspec-

tive, running just one piece of code at a time seems silly. But once you

understand event-driven programming—with nonblocking APIs—it becomes

clear.

Programming is chock-full of backwardisms like these, and Node.js is no

exception. Starting out, you’ll frequently run into code that looks like it should

work one way, but it actually does something quite different.

That’s OK! With this book, you’ll learn Node by making compact programs

that interact in useful ways. As we run into more of Node’s backwardisms,

we’ll dive in and explore them.

Aspects of Node.js Development

Node.js is a surprisingly big subject, so let’s break it down into different

aspects. There are many aspects of Node.js development we might talk about,

ranging from basic JavaScript syntax to revision control. This book focuses

on five in particular:

• Practical programming

• Architecture and core

• Patterns

• JavaScriptisms

• Supporting code

Let’s explore each of these briefly.

Practical Programming

Practical programming is all about producing real code that does something

useful. Interacting with a file system, establishing socket connections, or

serving web applications are all examples of practical programming.

Each of the remaining chapters of this book focuses on one particular practical

domain. Through code examples specific to each domain, you’ll learn Node’s

architecture, patterns, JavaScriptisms, and supporting code.

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Architecture and Core

Understanding Node’s architecture will help you to harness its features while

avoiding performance-crushing pitfalls. For example, Node uses an event loop

written in C for scheduling work. But it executes application code in a Java-

Script environment. How information is shuttled between these layers is the

kind of impactful architectural detail you’ll learn.

Patterns

Like any successful codebase with a healthy ecosystem, Node.js has a number

of repeating patterns. Some of these patterns are baked into the core while

others mostly appear in third-party libraries. Examples include the use of

callbacks, error-handling techniques, and classes like

EventEmitter

and

Stream

which are used liberally for event dispatching.

As we progress through different practical programming domains, we’ll natu-

rally encounter these and other patterns. When we do, you’ll discover why

they’re useful and how to use them effectively.

JavaScriptisms

JavaScript is the language of Node programs, so you’ll be seeing quite a lot

of it. The code examples in this book make use of the latest available Java-

Script features. Some of these features may be unfamiliar to you, even if

you’ve done JavaScript development before.

JavaScriptisms discussed in this book include things like the nature of

functions and object inheritance. ECMAScript Harmony—the code name for

the next version of the JavaScript spec—packs some new features we’ll use,

too.

Supporting Code

Code does not live in isolation; it takes a village to support any individual

program. Supporting code covers lots of things, from unit testing to perfor-

mance benchmarks to deployment scripts. We’ll use supporting code

throughout the book to make our programs more robust, more scalable, and

more manageable.

With these five aspects, you’ll be able to develop applications that make the

most use out of the platform while using idiomatic Node.js style. The example

applications you’ll develop in this book are functional and small, and aim to

clearly demonstrate the five aspects. But to use them, you’ll need to get Node.js

installed first.

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