JavaScript Ninja的秘密：跨浏览器技巧与测试实战

JavaScript

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《JavaScript Ninja的秘密》是一本2012年英文版的专业书籍，专为JavaScript开发者提供深入且实用的知识。本书由MEAP（Manning Early Access Program）出版，Manning Publications是其发行商，如需了解更多该出版社的其他作品，请访问www.manning.com。本书分为四个章节，每个章节都针对JavaScript的重要概念进行详尽解析： 1. **引言与JavaScript语言基础**：首先介绍了JavaScript语言的基本概念，让读者对这门动态脚本语言有一个全面的认识。作者强调了编写跨浏览器兼容代码的最佳实践，帮助开发者理解和掌握JavaScript在不同环境中的行为差异。 2. **测试与调试**：这一章深入探讨了测试和调试的重要性。内容包括调试代码的方法、如何选择合适的测试套件，如QUnit、YUITest和JSUnit等工具的使用。此外，还讲解了测试套件的基础原则，如断言机制、测试组的组织以及异步测试的处理。通过这些技巧，开发者可以提高代码质量并提升问题定位能力。 3. **函数与编程技巧**：本章详细讲解了函数的各种用法，包括函数定义、匿名函数、递归、函数作为对象、存储函数、自memoizing函数、上下文管理、循环、模拟数组方法、可变参数、数组操作（如找到最大最小值）、函数重载、函数长度和类型判断等。这些技能对于构建高效、灵活的代码至关重要。 4. **闭包与高级编程技术**：深入剖析了闭包的工作原理，如何利用它们创建私有变量和实现数据封装。同时，讨论了回调函数和定时器在闭包中的应用，以及如何通过函数作用域控制、部分应用函数、改变函数行为、记忆化和函数包装等技术优化代码。章节最后，通过一个常见的匿名函数执行示例，展示了临时作用域和私有变量的使用。《Secrets of the JavaScript Ninja》不仅提供了基础知识，还涵盖了现代JavaScript开发中的高级实践，帮助开发者提升技能，解决实际项目中的复杂问题，从而成为真正的JavaScript ninja。

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Testing and Debugging

• Your tests should be highly reproducible. It should be possible to run your test over and over and

never receive a different result. Additionally this includes making sure that your tests aren't dependent

upon outside issues like network or CPU load.

• Your tests should be as simple as possible. You should strive to remove as much HTML markup,

CSS, or JavaScript as you can without disrupting the original test case. The more that you can remove

the greater the likelihood that the test case will only be influenced by the exact bug that you're trying

to detect.

• Break tests apart. Try not to make the results from one test be dependent upon another. Break tests

down into their smallest possible unit (which helps you to determine the exact source of a bug when

an error occurs).

With those points in mind, let's look at the two techniques for developing test cases:

Deconstructive Test Cases

Deconstructive test cases center around the use of an existing site or page that exhibits an issue and tearing

it down to only show the representative problem. This is the ultimate case of applying the above points to

test generation. You might start with a complete site but after removing extra markup, CSS, and JavaScript

you'll arrive at a smaller site that reproduces the problem. You continue the process until no more code

can be removed.

Constructive Test Cases

With a constructive test case you start from a known, reduced, case and build up until you're able to

reproduce the bug in question. In order to do this style of testing you'll need a couple simple test files from

which to build and a way to generate these new tests with a clean copy of your code.

For example, when I'm attempting to create reduced test cases I'll end up having a few HTML files with

minimum functionality already included in them (one for DOM manipulation, one for Ajax tests, one for

animations, etc.). For example, in Listing 1-2, is the simple DOM test case that I use.

Listing 1-2: A reduced DOM test case for jQuery.

$(document).ready(function(){

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

});

</script>

<style>

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

</style>

To generate a test, with a clean copy of the code base, I use a little shell script to check the library, copy

over the test case, and build the test suite, as shown in Listing 1-3.

Listing 1-3: A simple shell script used to generate a new test case.

#!/bin/sh

# Check out a fresh copy of jQuery

git clone git://github.com/jquery/jquery.git $1

# Copy the dummy test case file in

cp $2.html $1/index.html

Testing and Debugging

The vast majority of the those testing JavaScript used one of four tools (all of which were virtually tied

in the results at various points in time): JSUnit, QUnit, Selenium, and YUITest. That alone was quite

interesting, there hasn't been any definitive collection of the major testing frameworks until this point, but

even more interesting was the massive "long tail" of one-off frameworks that have one, or very few, users.

It should be noted that it's incredibly easy for someone to write a testing framework from scratch and

that they should as it'll help them to gain a greater understanding of what a testing framework is trying

to achieve. This is an especially interesting challenging to tackle because when you're writing a testing

framework you typically don't have to deal with many cross-browser issues and it's a relatively painless,

but informative, exploration (unless you're trying to simulate browser events, then good luck).

Obviously a number of people have come to this same conclusion and have written a large number of one-

off frameworks to suite their own particular needs. The diminished number of cross-platform issues makes

this merely an engineering challenge rather than one of rote browser-bug-battling.

General JavaScript unit testing frameworks tend to provide a few basic components: A test runner, test

groupings, and assertions. Some also provide the ability to handle asynchronously-run tests.

While it is quite easy to write your own unit testing framework it's likely that you'll just want to use

something that's been pre-built. In that case I recommend checking out some of the most popular unit

testing frameworks.

QUnit

QUnit is the unit testing framework that was originally built to test the jQuery framework. It has since

expanded beyond its initial goals and is now a standalone unit testing framework. QUnit is primarily

designed to be a simple solution to unit testing, providing a reduced (but easy to use) API.

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JavaScript Ninja的秘密：跨浏览器技巧与测试实战

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