Beginning JavaScript with DOM Scripting and Ajax: 免费电子书下载

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"《 Beginning JavaScript with DOM Scripting and Ajax 第二版》是一本专注于JavaScript、DOM脚本和Ajax技术的入门教程。作者通过深入浅出的方式，引导读者理解和应用这些核心技术，提升Web开发技能。书中涵盖了从基础的JavaScript语法到复杂的Ajax交互，以及数据验证和第三方JavaScript库的使用。" 本书旨在帮助初学者掌握JavaScript编程语言，了解DOM（Document Object Model）的概念，并学习如何利用Ajax进行无刷新页面更新。JavaScript是网页动态效果和交互性的重要工具，DOM则是HTML和XML文档的结构化表示，允许开发者通过编程方式操作网页元素。Ajax技术则使得网页可以在不重新加载整个页面的情况下与服务器交换数据并更新部分网页内容，提高了用户体验。在书中，第一章介绍了JavaScript的基础知识，包括变量、数据类型、条件语句和循环等。第二章深入讨论了数据处理和决策逻辑。第三章将焦点转向DOM，讲解了如何使用JavaScript操作DOM元素，实现动态网页效果。第四章结合HTML，讨论了如何在HTML文档中嵌入和使用JavaScript。第五章探讨了CSS和事件处理，展示了如何分离样式和行为，以及如何响应用户交互。第六章介绍了图像和窗口的JavaScript应用。第七章讲解了导航和表单的处理，这是用户界面交互的关键部分。第八章则进入了Ajax的世界，介绍了如何使用Ajax与服务器进行后台交互，并涉及了Node.js的基础知识。第九章探讨了数据验证技术，这对于确保用户输入的有效性和安全性至关重要。第十章通过一个现代JavaScript案例研究——动态画廊，展示了实际项目中的应用。最后，第十一章讨论了如何利用第三方JavaScript库，如jQuery等，来加速开发进程。此外，书中还包含了一个专门的附录，介绍了JavaScript的调试技巧，帮助读者解决在开发过程中遇到的问题。书末的索引方便读者查找特定主题。这是一本全面且实用的JavaScript学习资源，适合想要提升Web开发技能的初学者和专业人士。

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CHAPTER 1 ■ GETTING STARTED WITH JAVASCRIPT

Note that you’re measuring the screen size here, and the user might have a 800×600 screen, but that doesn’t

mean his browser window is maximized. You might be applying a style that is not appropriate.

You’re using another object, the document object, to write to the page (an HTML document). The document

object’s write() method allows you to insert HTML into the page. Note that document.write() doesn’t actually

change the source HTML page, just the page the user sees on his computer.

Note ■ In fact, you’ll find document.write() very useful as you work through the first few chapters of the book. It’s

good for small examples that show how a script is working, for communicating with the user, and even for debugging an

area of a program that you’re not sure is doing what you think it should be doing. It also works on all browsers that support

JavaScript. More modern browsers have better tools and methods for debugging, but I’ll say more on that later in the book.

You use document.write() to write out the appropriate link element with your defined style in the head:

document.write( '<link rel="StyleSheet" href="' +

cssName + '" type="text/css" />' );

And in the document’s body, you write out the message explaining which resolution style was applied:

document.write( '<p>Applied Style: '+ resolutionInfo + '</p>' );

</script>

Later on, we’ll work with more complex examples that use JavaScript to test capabilities of the user’s agent and

interface. For now, though, I hope this simple example gives you an inkling of the kind of flexibility you can add to

your web pages using JavaScript.

Summary

In this chapter, we took a look at what JavaScript is, how it works, and what its advantages and disadvantages are.

I noted that the biggest disadvantage is that you cannot rely on it as a given. However, I also mentioned that using

JavaScript can make web sites a nicer and slicker experience for your users.

You ran some JavaScript code, saw how to add comments to the code, and saw how to separate JavaScript

statements using semicolons. You also saw that you can tell JavaScript to treat a group of lines of code as a single block

using curly braces, following an if statement, for example. You learned that JavaScript execution generally runs from

top to bottom, and from the first script block to the last, with the exception of functions that execute only when you

tell them to.

You also looked at objects, which are central to writing JavaScript. Not only is JavaScript itself very much

dependent on objects, but the browser also uses objects and methods to make itself and the document available for

scripting. Finally, you looked at a simple example that reads out the user’s screen resolution and applies a suitable

style sheet.

In the next chapter, I’ll cover the language fundamentals of JavaScript. You’ll see how JavaScript stores and

manipulates data, and uses it in calculations. We’ll also look at creating “intelligent” JavaScript programs using

decision-making statements that allow you to evaluate data, do calculations with it, and decide on an appropriate

course of action. With that chapter under your belt, you’ll have most of the fundamental knowledge needed to go on

to more exciting and useful web programming.

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Chapter 2

Data and Decisions

Data and decision making are fundamental to every intelligent program. We’ll begin this chapter by looking at how

JavaScript understands, or represents, data. This is important because JavaScript works with a number of data types and

manipulates data according to its data type. You can generate unexpected results by mismatching data of different types.

We’ll look at some of the more common data type problems, and you’ll see how to convert one type of data to another.

We’ll also be working with conditional statements and loops: two of the most valuable tools for decision making.

To make decisions in a computer language, you need to let the program know what should happen in response to

certain conditions, which is where conditional statements come in. Loops, on the other hand, simply allow you to

repeat an action until a specified circumstance is met. For example, you might want to loop through each input box in

a form and check that the information it contains is valid.

I’ll be covering a lot of different facets of JavaScript in this chapter:

Classifying and manipulating information in JavaScript: data types and data operators•

Variables•

Converting data types•

Introducing data objects: • String, Date, and Math objects

Arrays: storing ordered sets of data, like the items in a shopping basket•

Decision making with conditional statements, loops, and data evaluation•

Note ■ The examples in this chapter are kept as simple as possible and therefore use document.write() as a

feedback mechanism for you to see the results. You’ll learn in later chapters about other methods for doing this that are

more modern and versatile.

Data, Data Types, and Data Operators

Data is used to store information, and to do that more effectively, JavaScript needs to have each piece of data assigned

a type. This type stipulates what can or cannot be done with the data. For example, one of the JavaScript data types is

number, which you can use to perform certain calculations on the data that it holds.

The three most basic data types that store data in JavaScript are

• String: A series of characters—for example, "some characters"

• Number: A number, including floating point numbers

• Boolean: Can contain a true or false value

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CHAPTER 2 ■ DATA AND DECISIONS

These are sometimes referred to as primitive data types, because they store only single values. There are two

slightly different primitive data types as well. These don’t store information, but instead warn you about a

particular situation:

• Null: Indicates that even though a variable has been created, its current value is null or

nothing.

• Undefined: Indicates that something has not been defined and given a value. This is

important when you’re working with variables.

We’ll be working extensively with these data types throughout the chapter.

The String Data Type

The JavaScript interpreter expects string data to be enclosed within single or double quotation marks (known as

delimiters). The following script, for example, will write some characters on the page:

<html>

<body>

document.write("some characters");

</script>

</body>

</html>

The quotation marks won’t be written to the page because they are not part of the string; they simply tell

JavaScript where the string starts and ends. You could just as easily use single quotation marks:

<html>

<body>

document.write('some characters');

</script>

</body>

</html>

Both methods are fine, as long as you close the string the same way you opened it and don’t try to delimit it

like this:

document.write('some characters");

document.write("some characters');

Of course, you might want to use a single or double quotation mark inside the string itself—in which case, you

need to use a distinct delimiter. If you use double quotation marks, the instructions will be interpreted as you intended:

document.write("Paul' s characters");

But if you used single quotations marks, they won’t be:

document.write('Paul' s characters');

This gives you a syntax error because the JavaScript interpreter thinks the string ends after the l in Paul and

doesn’t understand what is happening afterwards.

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