javascript忍者秘籍：深入解析与实践

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"《JavaScript Ninja的秘密》是一本深入探讨JavaScript编程的高级指南，由Manning Publications出版，版权于2012年。本书旨在帮助开发者掌握JavaScript语言的精髓，通过一系列实战技巧和策略，提升在实际项目中的编码能力。以下是部分内容概览： 1. **进入忍者世界**：章节标题暗示读者将学习如何成为JavaScript编程领域的高手，可能包括对基础语法和最佳实践的介绍。 2. **测试与调试**：这部分涵盖了如何有效地进行代码测试和定位错误，以确保程序的稳定性和可靠性。 3. **函数的力量**：JavaScript函数是核心概念，作者会讲解函数的使用、作用域和闭包，这些都是高级编程的基础。 4. **操控函数**：深入理解函数的工作原理，如高阶函数、柯里化等，以提高代码的复用性和灵活性。 5. **闭包的秘密**：探索JavaScript中闭包的复杂性，了解其如何保存状态和创建私有变量。 6. **原型与面向对象**：阐述JavaScript的对象模型，包括原型链和原型继承，以及如何设计面向对象的解决方案。 7. **正则表达式大师**：细致讲解如何编写高效且易读的正则表达式，以便在文本处理和数据验证中得心应手。 8. **多线程与定时器**：涉及异步编程和事件循环，帮助开发者理解和管理JavaScript中的并发与延迟行为。 9. **运行时代码评价（Ninja Alchemy）**：探讨动态代码加载和eval函数的使用及其潜在风险，强调安全编程的重要性。 10. **with语句的使用与陷阱**：分析with语句的优缺点，以及何时应该避免或谨慎使用。 11. **跨浏览器开发策略**：提供针对不同浏览器兼容性的解决方案，确保代码能在多种环境正常工作。 12. **属性、属性与CSS**：深入解析JavaScript中关于对象属性的访问、操作和CSS选择器的运用。 13. **事件处理的艺术**：讲解如何优雅地处理用户交互，包括事件冒泡、捕获和委托等。 14. **DOM操作进阶**：提供高级DOM操作技术，如节点遍历、事件绑定和DOM修改。 15. **CSS选择器引擎揭秘**：剖析浏览器内部如何解析和应用CSS选择器，这对于理解样式渲染至关重要。作为Manning Early Access Program的一部分，读者可以访问在线论坛（<http://www.manning-sandbox.com/forum.jspa?forumID=431>），发表评论和交流学习心得。这本PDF提供了丰富的资源，适合希望成为JavaScript高手的开发人员不断精进自己的技能。"

©Manning Publications Co. Please post comments or corrections to the Author Online forum:

http://www.manning-sandbox.com/forum.jspa?forumID=431

Note how the rightmost pane allows us to see the state within which our code is running,

including the value of

The debugger breaks on a line before that line is actually executed; so in this example,

the call to our

log() method has yet to be executed. If we were to imagine that we were

trying to debug a problem with our new method, we might want to step into that method to

see what’s going on inside it.

Clicking on the “step into” button (left-most gold arrow button) causes the debugger to

execute up to the first line of our method, and we’d see the display of figure 2.3.

Figure 2.3 Stepping into our method lets us see the new state within which the method executes

Note how the displayed state has changed to allow us to poke around the new state

within which our

log() method executes.

Any fully featured debugger with breakpoint capabilities is highly dependent upon the

browser environment in which it is executing. For this reason, the aforementioned developer

tools were created as the functionality provided by them would not be otherwise possible. It

is a great boon and relief to the entire web development community that all the major

browser implementers have come on board to create effective utilities for allowing debugging

activities.

Debugging code not only serves its primary and obvious purpose (detecting and fixing

bugs), it also can helps us achieve the good practice goal of generating effective test cases.

2.2 Test generation

Robert Frost wrote that good fences make good neighbors, but in the world of web

applications, indeed any programming discipline, good tests make good code.

Note the emphasis on the word good. It’s quite possible to have an extensive test suite

that doesn’t really help the quality of our code one iota if the tests are poorly constructed.

Good tests exhibit three important characteristics:

• Repeatability – our test results should be highly reproducible. Tests run repeatedly

should always produce the exact same results. If test results are nondeterministic,

how would we know what are valid results versus invalid results? Additionally this

Licensed to <pedbro@gmail.com>

©Manning Publications Co. Please post comments or corrections to the Author Online forum:

http://www.manning-sandbox.com/forum.jspa?forumID=431

helps to make sure that your tests aren't dependent upon external factors issues like

network or CPU loads.

• Simplicity – our tests should focus on testing one thing. We should strive to

remove as much HTML markup, CSS, or JavaScript as we can without disrupting the

intent of the test case. The more that we remove, the greater the likelihood that the

test case will only be influenced by the specific code that we are trying to test.

• Independence – our tests should execute in isolation. We must strive to not make

the results from one test be dependent upon another. We should break tests down

into their smallest possible unit, which helps us to determine the exact source of a bug

when an error occurs.

There are a number of approaches that can be used for constructing tests, with the two

primary approaches being: deconstructive tests and constructive tests. Let’s examine what

each of these approaches entails:

 Deconstructive test cases

Deconstructive test cases are created when existing code is whittled down

(deconstructed) to isolate a problem, eliminating anything that’s not germane to the

issue. This helps us to achieve the three characteristics listed above. We might start

with a complete site, but after removing extra markup, CSS, and JavaScript, we arrive

at a smaller case that reproduces the problem.

 Constructive test cases

With a constructive test case you start from a known good, reduced case and build up

until we're able to reproduce the bug in question. In order to use this style of testing

we'll need a couple simple test files from which to build up tests, and a way to

generate these new tests with a clean copy of your code.

Let’s see an example of constructive testing.

When creating reduced test cases, we can start with a few HTML files with minimum

functionality already included in them. We might even have different starting files for various

functional areas; for example, one for DOM manipulation, one for Ajax tests, one for

animations, and so on.

For example, Listing 2.3 shows a simple DOM test case used to test jQuery.

Listing 2.3: A reduced DOM test case for jQuery

<<script src="dist/jquery.js"></script>

$(document).ready(function() {

$("#test").append("test");

});

</script>

<style>

#test { width: 100px; height: 100px; background: red; }

</style>

Licensed to <pedbro@gmail.com>

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