Node.js设计基础与实战

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"Node.js Web开发相关资源，包括作者简介、书摘、书籍概述和Node.js设计模式介绍" 在本资源包中，您将获取关于Node.js Web开发的关键信息。Node.js是一个基于Chrome V8引擎的JavaScript运行环境，它允许开发者使用JavaScript进行服务器端编程，从而打破了JavaScript只能在浏览器中运行的传统限制。Node.js以其非阻塞I/O和事件驱动的特性，成为构建高性能网络应用的理想选择。作者Mario Casciara是一位热衷于开源软件的软件工程师和技术主管。他的编程生涯始于12岁时的Commodore 64，随着技术的发展，他掌握了Pascal、Visual Basic、C、C++、PHP和Java等语言。在对JavaScript和Node.js的探索中，他找到了新的编程热情。在IBM工作期间，Mario涉及了多种技术，如C、PHP和Java，并参与了Tivoli、Cognos和Collaboration Solutions等产品的开发。随后，他投身创业领域，专注于全职的Node.js项目，特别是在D4H Technologies，领导了一个实时应急操作管理平台的开发。资源中包含的"Node.js设计基础"章节，可能涵盖了Node.js的核心概念，如事件循环、异步编程、模块系统以及性能优化策略。书的概述部分将向读者介绍全书的主要内容，可能包括Node.js架构、Web服务器的创建、数据处理、错误处理、安全性以及如何利用Node.js构建可扩展的应用。此外，对于那些想要深入了解Node.js设计模式的人来说，资源中提供的信息将非常有价值。设计模式是解决特定问题的通用解决方案，它们在Node.js中的应用可以帮助开发者编写更高效、可维护的代码。可能涵盖的主题包括单例模式、工厂模式、观察者模式等，这些模式在构建复杂的Node.js应用程序时尤其有用。这个资源为Node.js初学者和经验丰富的开发者提供了宝贵的资料，无论是在理论知识还是实践经验上，都能得到提升。通过学习书中的内容，开发者可以更好地理解如何利用Node.js的特性来构建高性能、实时的Web应用。

Node.js Design Fundamentals

[ 10 ]

Another characteristic of many Node.js modules is the fact that they are created to

be used rather than extended. Locking down the internals of a module by forbidding

any possibility of an extension might sound inﬂ exible, but it actually has the

advantage of reducing the use cases, simplifying its implementation, facilitating its

maintenance, and increasing its usability.

Simplicity and pragmatism

Have you ever heard of the Keep It Simple, Stupid (KISS) principle? Or the

famous quote:

"Simplicity is the ultimate sophistication."

– Leonardo da Vinci

Richard P. Gabriel, a prominent computer scientist coined the term worse is better to

describe the model, whereby less and simpler functionality is a good design choice

for software. In his essay, The rise of worse is better, he says:

"The design must be simple, both in implementation and interface. It is more

important for the implementation to be simple than the interface. Simplicity is

the most important consideration in a design."

Designing a simple, as opposed to a perfect, feature-full software, is a good

practice for several reasons: it takes less effort to implement, allows faster shipping

with less resources, is easier to adapt, and is easier to maintain and understand.

These factors foster the community contributions and allow the software itself to

grow and improve.

In Node.js, this principle is also enabled by JavaScript, which is a very pragmatic

language. It's not rare, in fact, to see simple functions, closures, and object literals

replacing complex class hierarchies. Pure object-oriented designs often try to

replicate the real world using the mathematical terms of a computer system without

considering the imperfection and the complexity of the real world itself. The truth is

that our software is always an approximation of the reality and we would probably

have more success in trying to get something working sooner and with reasonable

complexity, instead of trying to create a near-perfect software with a huge effort and

tons of code to maintain.

Throughout this book, we will see this principle in action many times. For example,

a considerable number of traditional design patterns, such as Singleton or Decorator

can have a trivial, even if sometimes not foolproof implementation and we will see

how an uncomplicated, practical approach most of the time is preferred to a pure,

ﬂ awless design.

Chapter 1

[ 11 ]

The reactor pattern

In this section, we will analyze the reactor pattern, which is the heart of the Node.js

asynchronous nature. We will go through the main concepts behind the pattern,

such as the single-threaded architecture and the non-blocking I/O, and we will

see how this creates the foundation for the entire Node.js platform.

I/O is slow

I/O is deﬁ nitely the slowest among the fundamental operations of a computer.

Accessing the RAM is in the order of nanoseconds (10e

-9

seconds), while accessing

data on the disk or the network is in the order of milliseconds (10e-3 seconds). For

the bandwidth, it is the same story; RAM has a transfer rate consistently in the order

of GB/s, while disk and network varies from MB/s to, optimistically, GB/s. I/O

is usually not expensive in terms of CPU, but it adds a delay between the moment

the request is sent and the moment the operation completes. On top of that, we also

have to consider the human factor; often, the input of an application comes from a

real person, for example, the click of a button or a message sent in a real-time chat

application, so the speed and frequency of I/O don't depend only on technical

aspects, and they can be many orders of magnitude slower than the disk or network.

Blocking I/O

In traditional blocking I/O programming, the function call corresponding to an

I/O request will block the execution of the thread until the operation completes.

This can go from a few milliseconds, in case of a disk access, to minutes or even

more, in case the data is generated from user actions, such as pressing a key. The

following pseudocode shows a typical blocking read performed against a socket:

//blocks the thread until the data is available

data = socket.read();

//data is available

print(data);

It is trivial to notice that a web server that is implemented using blocking I/O will

not be able to handle multiple connections in the same thread; each I/O operation

on a socket will block the processing of any other connection. For this reason, the

traditional approach to handle concurrency in web servers is to kick off a thread

or a process (or to reuse one taken from a pool) for each concurrent connection

that needs to be handled. This way, when a thread blocks for an I/O operation

it will not impact the availability of the other requests, because they are handled

in separate threads.

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