HTML、JavaScript与PHP编程指南：面向科学家与工程师的实用教程

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"《HTML、JavaScript与PHP指南》是一本专为科学家和工程师设计的实用手册，旨在帮助他们解决计算机上的计算问题，特别是在无需深入了解编程语言原理的情况下。对于那些主要关注科学或工程领域，而非计算机科学或计算机工程的学生和专业人士来说，选择学习HTML、JavaScript和PHP可能更具吸引力。 HTML被广泛用于开发独立的在线应用程序，其易用性和普遍性使得科学家和工程师能够轻松创建交互式网页和动态内容。JavaScript则在此基础上更进一步，提供了一种在客户端处理用户交互的能力，例如验证表单、动画效果和数据处理等。然而，JavaScript的功能受限于它与服务器端数据交互的局限性，这就引出了PHP的重要性。 PHP作为一种服务器端脚本语言，弥补了JavaScript的不足，允许开发者访问和操作外部存储的数据文件，这极大地扩展了解决科学和工程问题的范围。学习这些Web基础语言，如HTML、JavaScript和PHP，对任何科学家或工程师而言都是一项宝贵技能，因为它们不仅能满足实际工作需求，而且由于其基于Web的特性，相对于传统的文本为基础的语言，这些技能可能更容易在市场上找到应用。本书作者David R. Brooks假设，通过学习如何在在线环境中使用这三种语言，学生和专业人员可能会认为这是一个更为相关且实用的学习路径。对于学生们来说，虽然没有完美的解决方案来平衡编程语言的掌握，但HTML、JavaScript和PHP的学习无疑提供了一个既能满足实际需求又能体现相关性的选择。《HTML、JavaScript和PHP指南》不仅介绍了这些技术的基础知识，还涵盖了如何在实践中运用它们来解决科学和工程领域的具体问题，帮助读者提升在数字化世界中的问题解决能力。对于那些希望在这个快速发展的技术环境中保持竞争力的读者，这是一本不可多得的参考书。"

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D.R. Brooks, Guide to HTML, JavaScript and PHP: For Scientists and Engineers,

DOI 10.1007/978-0-85729-449-4_1, © Springer-Verlag London Limited 2011

Introducing HTML and JavaScript

Abstract Chapter 1 provides a very brief introduction to using HTML and JavaScript for

creating simple Web pages. It presents examples of how JavaScript interfaces with an

HTML document to display some printed output in a Web browser window. The chapter

introduces the concept of an HTML document as an object, with certain methods and

properties accessible through JavaScript to act on that object.

Numerous examples show how to modify the appearance of a document by using

HTML tags and their attributes, including as part of a text string passed as a calling argu-

ment to JavaScript’s write() method.

1.1

Introducing the Tools

1.1.1

What Is an HTML Document?

HTML is an acronym for HyperText Markup Language. HTML documents, the foun-

dation of all content appearing on the World Wide Web (WWW), consist of two essen-

tial parts: information content and a set of instructions that tells your computer how to

display that content. The instructions—the “markup,” in editorial jargon—comprise the

HTML language. It is not a programming language in the traditional sense, but rather a

set of instructions about how to display content. The computer application that translates

this description is called a Web browser. Ideally, online content should look the same

regardless of the operating system on which a Web browser resides or the browser used.

This goal of complete platform independence is achieved only approximately in

practice.

A basic HTML document requires a minimum of four sets of elements:

2 1 Introducing HTML and JavaScript

These elements dene the essential parts of an HTML document: the document itself, a

heading section, a title section, and a body. Each of the elements is dened by two tags—a

start tag and an end tag. Tags are always enclosed in angle brackets: <…>. End tags start

with a slash (/). As will be shown later, some HTML elements have only one tag. Most

tags are supposed to occur in pairs, although this rule is enforced only loosely in HTML.

In order to support a scripting language such as JavaScript (much more about that later!),

another element must be added to the four basic elements:

As used in this book, a script element always contains JavaScript code.

These elements are organized as follows within an HTML document:

<html>

<head>

…

</head>

<body>

…

</body>

</html>

The html tag encloses all other tags and denes the boundaries of the HTML docu-

ment. We will return to the other tags later. script tags often appear inside the <head>

tag, but they can appear elsewhere in a document, too. The indenting used to set off pairs

of tags is optional, but it makes documents easier to create, read, and edit. This style is part

of good programming practice in all languages.

Because JavaScript is so tightly bound to HTML documents, you must learn JavaScript

along with at least a subset of HTML. Unfortunately for anyone trying to learn and use

HTML and JavaScript, each of the several available browsers is free to implement and sup-

port JavaScript in its own way. A browser doesn’t even have to support JavaScript at all,

although it is hard to imagine why it wouldn’t. Browsers can and do incorporate some pro-

prietary HTML and JavaScript features that may not be supported by other browsers. Newer

versions of any browser may support features that won’t be recognized by earlier versions.

Fortunately, it is possible to work with what is essentially a de facto standardized subset

of HTML and JavaScript. As a result, some of the descriptions of the details of HTML and

JavaScript in this book will be incomplete; this is not necessarily a bad thing!

Although HTML documents are usually considered to be a way of distributing informa-

tion for remote access on the Web, they are equally useful when used locally on any com-

puter that has a browser. So, in conjunction with JavaScript (and later with PHP), you can

create a self-contained problem-solving environment that can be used locally as well as

(literally) globally.

31.1 Introducing the Tools

Good programming technique often involves separating the input/output (I/O)

interface from the underlying calculations that do the work of a program. The program-

ming environment provided by HTML/JavaScript provides a conceptually elegant means

of implementing this strategy. An HTML document provides the I/O interface and

JavaScript (and/or PHP, as will be seen later in this book) handle the calculations. An

advantage of HTML is that it provides a wealth of interface possibilities that far surpass

those of text-based languages such as C.

1.1.2

What Is JavaScript?

JavaScript is an interpreted (rather than compiled) object-oriented programming language

that has been developed for use alongside other Web tools. JavaScript does not operate as

a standalone language. It is designed to work together with HTML for creating interactive

Web pages. It is not the same as Java, which is a compiled object-oriented language.

JavaScript is used to write client side applications, which means that JavaScript code

is sent to a user’s computer when a Web page is loaded. The code is then executed, basi-

cally line by line, by a JavaScript interpreter included as part of the user’s (client’s) Web

browser. This arrangement minimizes security issues that can arise when a client computer

interacts with the computer that sent the page. It also makes it easy to package an entire

problem, with its own user interface and solution, self-contained within a single document.

But the inability to interact dynamically with information stored on a server imposes limi-

tations on the kinds of tasks that JavaScript can accomplish.

It is commonplace to refer to any set of written computer instructions as a “program.”

However, this term is more rigorously applied to a separate entity that can be executed on its

own. Because JavaScript is interpreted rather than compiled, a separately executable entity is

never created. Instead, JavaScript code statements are interpreted and executed one at a time,

essentially “on the y.” Although this may seem inefcient, there is rarely any discernible

time lag associated with executing JavaScript commands on modern computers.

JavaScript is one of a class of scripting languages whose purpose is to access and mod-

ify components of an existing information interface. (Microsoft’s VBScript is another

scripting language.) In this case, the interface is an HTML document. As soon as HTML

documents on the Web evolved from one-way delivery systems for displaying xed con-

tent, something like JavaScript immediately became necessary. One of its rst applications

arose from the need to check values entered by users into the elds of HTML forms that

can be sent back to the originator. (Forms are discussed in a later chapter.) JavaScript can

be used to compare input values against an expected range or set of values and to generate

appropriate messages and other actions based on those comparisons.

JavaScript has evolved into a complete programming language with extensive capabili-

ties for manipulating text and handling mathematical operations, useful for a wide range of

computing problems. Possible applications include many self-contained scientic and

engineering calculations. As noted earlier, JavaScript is restricted to problems that do not

need to access external data sources, regardless of whether those sources reside on a local

computer or on a remote server.

4 1 Introducing HTML and JavaScript

As previously noted, the major challenge in learning HTML/JavaScript is that it is not

a completely standardized environment. The various dialects of HTML and JavaScript

pose problems even for experienced programmers. These kinds of problems can be mini-

mized by focusing on an appropriate subset of HTML/JavaScript. This is feasible because

there is little reason to use browser-specic subsets of HTML/JavaScript in the context of

the topics dealt with in this book.

1.1.3

How Do You Create HTML/JavaScript Documents?

Because HTML/JavaScript documents are just text documents, they can be created with

any text editor. Even Windows’ very basic Notepad application is a workable choice for

simple tasks.

Once they are created, you can open HTML les in your computer’s

browser—hopefully without regard to which browser you are using. As long as you give

such documents an .htm or .html le name extension, they should automatically open

in your browser when you double-click on the le name. Although Windows documents

are no longer restricted to three-letter extensions, a convention that dates back to the pre-

Windows days of the MS-DOS operating systems, the three-letter .htm extension is often

used on Windows systems. The four-letter .html extension is commonly used on UNIX

systems.

There is one other consequence of using Windows computers for creating all the code

examples in this text: Windows le names are case-insensitive, while in UNIX, all spell-

ings, including le names and commands, are case-sensitive. This shouldn’t cause prob-

lems, but it is something to keep in mind. In Windows, you can name a document

newDocument.htm. Later, you can spell it newdocument.htm, NEWDOCUMENT.

HTM, or any other combination of uppercase and lowercase letters and it won’t matter. On

a UNIX system, that le can be accessed only with the original spelling.

Although you can create text (and, therefore, HTML) documents with a full-featured

word processor such as Microsoft Word, this is not recommended. When you save a word

processor document it no longer contains just the text you have typed, but also all the lay-

out and formatting information that goes with that document. You can choose to save a

document as just text with an .htm extension, but it is easy to forget to do this.

Microsoft Word and other modern word-processing applications can also format any

document as an HTML document. However, this is also not recommended. These con-

verted documents may include a huge quantity of extraneous information and HTML

When you save a file in Notepad, the default extension is .txt. You may need to enclose the

file name plus its .htm extension in quote marks to prevent Notepad from adding the .txt

extension.

On Windows computers, you can associate extensions with whatever application you wish. So,

for example, if you have more than one browser installed on your computer, you could designate

one of them as the default browser and assign it as the application for opening HTML

documents.

51.1 Introducing the Tools

instructions that make the resulting le much larger and more complex than it needs to be.

(To see this for yourself, save a Word document as an HTML document and then look at

the result in a text editor such as Notepad!)

RTF (“rich text format”) documents are also unacceptable, as they still retain some

formatting information that is inappropriate for an HTML document. Any document that

contains “smart quotes” rather than "straight quotes" can also cause problems, because

smart quotes may not be displayed properly by browsers. (This is much less of a problem

on current browsers than it used to be.)

There are commercial Web development tools that allow you to create Web pages with-

out actually knowing anything about HTML or JavaScript. These applications are not

suitable for use with this book. The obvious reason is that the primary purpose of the book

is to show you how to write your own HTML documents and JavaScript code. Also, these

applications may create HTML les that are much larger and more complex than they need

to be for basic HTML documents. So, these applications are better suited for Web develop-

ment projects that involve a lot of graphics and the other “bells and whistles” that make

commercial Web pages attractive.

Creating an HTML/JavaScript document that works properly inevitably involves switch-

ing back and forth between a text editor and a browser—making changes and observing the

effects of those changes. Once you create a basic HTML document, you can open it in your

browser and move back and forth between this document and your text editor. Whenever you

change the document, you can reload or refresh it in your browser. It is certainly possible, but

not particularly convenient, to do this with a simple text editor such as Notepad.

There are many commercial software tools whose purpose is to facilitate writing and

editing HTML documents by integrating document creation, editing, and viewing. As

noted previously, some of them are intended for large and complicated projects and may

be “overkill” for use with this book. For several years, for creating this book and in my

own day-to-day work, I have used Visicom Media’s AceHTML Freeware V.5 (see www.

visicommedia.com). This software provides an HTML/JavaScript editor with some auto-

matic color-based text formatting that makes HTML instructions and JavaScript code

easier to read. There is an integrated browser, so it is easy to switch back and forth between

creating and editing a document and seeing the results of your work.

AceHTML also has a JavaScript syntax checker. As is typically the case, the checker

isn’t very good at telling you how to x a syntax error, but it at least tells you where the

error was detected. The freeware version of this editor may or may not be available cur-

rently, and it may require you to install other software that you may or may not want on

your computer. At the time this book was being published, freeware versions of AceHTML

were still available, as were versions available for purchase.

Although, in principle, it shouldn’t make any difference which browser you use, the

outputs displayed in this text come from either AceHTML’s internal browser or Mozilla’s

Firefox, which is the default browser on the author’s Windows computers. When you

Recent versions of AceHTML assume XHTML as the default language, rather than HTML. If

you use such a version with this book, you must override this assumption by saving files with

.htm or .html extensions.

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HTML、JavaScript与PHP编程指南：面向科学家与工程师的实用教程

Guide to HTML, JavaScript and PHP For Scientists and Engineers 无水印原版pdf

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