探索编程奥秘：《Eloquent JavaScript》现代入门指南

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《Eloquent JavaScript：现代编程入门》是由Marijn Haverbeke撰写的一本关于让计算机按照我们意愿工作的书籍。在21世纪，计算机已经变得非常普遍，但其内部的复杂性使得它们对许多人来说仍然是神秘且稍显威胁的存在。本书旨在简化这个过程，提供一个清晰、易懂的途径来学习编程。《Eloquent JavaScript》是一本现代化的编程指南，特别聚焦于JavaScript语言，这门在网页开发中不可或缺的语言。作者通过详尽的讲解和实例，引导读者理解编程的基本概念，如变量、数据类型、函数、控制结构、对象和类等，逐步深入到更高级的主题，如闭包、原型链、异步编程和正则表达式。版权方面，该书遵循Creative Commons Attribution-NonCommercial 3.0许可协议，允许用户在非商业用途下自由分享和改编内容。书中所有的代码同样受到MIT许可，这意味着可以根据开源原则进行使用和修改。此外，书中插图由多位艺术家创作，包括封面设计、各种角色形象（如电脑、无轮车人、海豚、松鼠、章鱼等）、正则表达式图示、游戏概念以及像素艺术等，丰富了阅读体验。第二版的出版得益于454位金融支持者的慷慨赞助，读者有机会购买纸质版，其中包含额外的附录章节，由No Starch Press印刷，可以在亚马逊购买链接中找到：[http://www.amazon.com/gp/product/1593275846/ref=as_li_qf_sp_asin_i]。《Eloquent JavaScript》是一本实用且易于上手的编程教程，适合初学者通过互动式学习和实践，掌握JavaScript编程的基础，从而更好地理解和操作这个无所不在的技术工具。无论你是想踏入编程世界的新手，还是希望提升JavaScript技能的开发者，这本书都是一个宝贵的学习资源。

proceed with caution and keep your wits about you. As you learn, there

will always be new challenges and new territory to explore. Program-

mers who refuse to keep exploring will stagnate, forget their joy, and get

bored with their craft.

Why language matters

In the beginning, at the birth of computing, there were no programming

languages. Programs looked something like this:

001 100 01 000 000 00 000 000 00

001 100 01 000 000 01 000 000 01

001 100 11 000 000 01 000 000 10

010 100 01 000 010 11 000 000 10

001 000 10 000 000 10 000 010 00

010 000 11 000 000 01 000 000 00

010 000 01 000 000 01 000 000 01

000 100 00 000 000 10 000 000 00

011 000 10 000 000 00 000 000 00

That is a program to add the numbers from 1 to 10 together and print

out the result (1 + 2 + ... + 10 = 55). It could run on a very simple,

hypothetical machine. To program early computers, it was necessary to

set large arrays of switches in the right position, or punch holes in strips

of cardboard and feed them to the computer. You can imagine how

this was a tedious, error-prone procedure. Even the writing of simple

programs required much cleverness and discipline. Complex ones were

nearly inconceivable.

Of course, manually entering these arcane patterns of bits (the ones

and zeros) did give the programmer a profound sense of being a mighty

wizard. And that has to be worth something in terms of job satisfaction.

Each line of the program above contains a single instruction. It could

be written in English like this:

1. Store the number 0 in m emor y l oca tio n 0.

2. Store the number 1 in m emor y l oca tio n 1.

3. Store the value of memo ry loca tion 1 in memory location 2.

4. Subt rac t the n umber 11 from the v alue in mem ory loc ati on 2.

5. If the v alue in mem ory loc ati on 2 is the num ber 0,

current generation of web applications possible—browser-based email

clients, maps, and social networks—and is also used in more traditional

sites to provide various forms of interactivity and cleverness.

It is important to note that JavaScript has almost nothing to do

with the programming language named Java. The similar name was in-

spired by marketing considerations, rather than good judgment. When

JavaScript was being introduced, the Java language was being heavily

marketed and was gaining in popularity. Someone thought it a good

idea to try to ride along on this success. Now we are stuck with the

name.

After its adoption outside of Netscape, a standard document was writ-

ten to describe the way the JavaScript language should work, to make

sure the various pieces of software that claimed to support JavaScript

were actually talking about the same language. This is called the EC-

MAScript standard, after the ECMA organization, which did the stan-

dardization. In practice, the terms ECMAScript and JavaScript can be

used interchangeably—they are two names for the same language.

There are those who will say terrible things about the JavaScript lan-

guage. Many of these things are true. When I was required to write

something in JavaScript for the ﬁrst time, I quickly came to despise it—

it would accept almost anything I typed but interpret it in a way that

was completely diﬀerent from what I meant. This had a lot to do with

the fact that I did not have a clue what I was doing, of course, but there

is a real issue here: JavaScript is ridiculously liberal in what it allows.

The idea behind this design was that it would make programming in

JavaScript easier for beginners. In actuality, it mostly makes ﬁnding

problems in your programs harder, because the system will not point

them out to you.

This ﬂexibility also has its advantages, though. It leaves space for a lot

of techniques that are impossible in more rigid languages, and, as we will

see, for example, in the

chapter on modules, it can be used to overcome

some of JavaScript’s shortcomings. After learning the language properly

and working with it for a while, I have learned to actually like JavaScript.

There have been several versions of JavaScript. ECMAScript version

3 was the dominant, widely supported version in the time of JavaScript’s

ascent to dominance, roughly between 2000 and 2010. During this time,

work was underway on an ambitious version 4, which planned a number

of radical improvements and extensions to the language. Changing a

living, widely used language in such a radical way turned out to be

politically diﬃcult, and work on the 4th edition was abandoned in 2008,

leading to the much less ambitious 5th edition coming out in 2009. We’re

now at the point where all major browsers support this 5th edition, which

is the language version that this book will be focusing on. A 6th edition

is in the process of being ﬁnalized, and some browsers are starting to

support new features from this edition.

Web browsers are not the only platforms on which JavaScript is used.

Some databases, such as MongoDB and CouchDB, use JavaScript as

their scripting and query language. Several platforms for desktop and

server programming, most notably the Node.js project, the subject of

Chapter 20, are providing a powerful environment for programming

JavaScript outside of the browser.

Code, and what to do with it

Code is the text that makes up programs. Most chapters in this book

contain quite a lot of it. In my experience, reading and writing code

is an indispensable part of learning to program. Try to not just glance

over the examples, read them attentively and understand them. This

will be slow and confusing at ﬁrst, but I promise that you will quickly

get the hang of it. The same goes for the exercises. Don’t assume you

understand them until you’ve actually written a working solution.

I recommend to try out your solutions to exercises in an actual JavaScript

interpreter, to get immediate feedback on whether what you are doing

is working or not, and, hopefully, to be tempted to experiment and go

beyond the exercises.

Most of the example code in this book can be found on the book’s

website, at eloquentjavascript.net/code, which also provides an easy way

to run the programs and experiment with writing your own code.

Running JavaScript programs outside of this book’s sandbox is also

possible. You can opt to install Node.js, and use it to run text ﬁles that

contain programs. Or you can use your browser’s developer console (typ-

ically found somewhere under a “tools” or “developer” menu) and play

around in there. In Chapter 12, the way in which JavaScript programs

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