深入学习jQuery英文原版PDF

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"Learning from jQuery 无水印原版pdf" 《Learning from jQuery》是一本由Callum Macrae编写的关于jQuery技术的书籍，旨在帮助读者深入理解和掌握jQuery这一广泛使用的JavaScript库。这本书的ISBN号是978-1-449-33519-9，版权归属Callum Macrae。本书可在多种PDF阅读器上正常打开，如FoxitReader、PDF-XChangeViewer、SumatraPDF和Firefox。 jQuery是一个轻量级、高性能的JavaScript库，它极大地简化了网页的DOM操作、事件处理、动画设计以及Ajax交互。在《Learning from jQuery》中，读者可以期待学习到以下关键知识点： 1. **jQuery基础**：了解如何引入jQuery库，以及如何选择和操作HTML元素，这是jQuery的基本功能，包括$(selector)的选择器语法和DOM遍历方法。 2. **事件处理**：jQuery提供了一套简洁的API来绑定和触发事件，书中会详细讲解如何使用`.on()`, `.click()`, `.hover()`等方法来处理各种用户交互。 3. **DOM操作**：学习如何使用jQuery修改DOM结构，添加、删除和修改元素，以及如何处理HTML内容和属性。 4. **CSS选择器**：jQuery扩展了标准的CSS选择器，让选取DOM元素更加灵活，书中会介绍这些高级选择器的用法。 5. **动画效果**：jQuery的动画功能强大，如`.fadeIn()`, `.slideUp()`, `.animate()`等，可以帮助创建流畅的过渡和效果。 6. **Ajax交互**：jQuery简化了Ajax请求，通过`.ajax()`, `.get()`, `.post()`等函数，可以轻松实现异步数据交换。 7. **插件开发与使用**：jQuery拥有庞大的插件生态系统，书中可能会涉及如何创建和使用第三方插件，以增强网站功能。 8. **性能优化**：理解如何有效利用jQuery进行性能优化，避免潜在的性能瓶颈，如延迟加载、事件委托等技术。 9. **兼容性与跨浏览器开发**：jQuery的一个主要优势是其良好的浏览器兼容性，书中会讨论如何处理不同浏览器之间的差异。 10. **最佳实践**：书中会提供一些编写高效、可维护的jQuery代码的最佳实践和建议。该书的第一版发布于2013年2月，对于初学者和有一定经验的开发者来说，都是一个宝贵的资源，可以帮助他们提升使用jQuery进行网页开发的技能。有兴趣的读者可以在美国亚马逊官网上找到更多关于本书的详细信息。

checks whether the .attachEvent method exists, and if so, then it calls function as

the handler. When the anonymous function is called, it calls the actual handler us-

ing .call, which allows us to specify the scope to be used as the first argument,

meaning that we can refer to the element using this.

To enable us to use the e.preventDefault() function in Internet Explorer, I’m adding

that function to the event, and when it is called, I’m setting e.returnValue to false.

We could also do this the other way around using the following, but I won’t be keeping

this code as we develop this function throughout the chapter because it isn’t standard-

conforming like e.preventDefault():

function addEventListener(element, event, handler) {

if (element.addEventListener) {

element.addEventListener(event, function (e) {

handler.call(this, e);

if (e.returnValue === false) {

e.preventDefault();

}

});

} else if (element.attachEvent) {

element.attachEvent('on' + event, function (e) {

handler.call(element, e);

});

}

That can be called as follows in any browser:

var foo = document.getElementById('foo');

addEventListener(foo, 'click', function (e) {

this.style.color = 'red';

e.returnValue = false;

});

We can also replicate jQuery’s return false behavior by checking the return value

of the event handler:

function addEventListener(element, event, handler) {

if (element.addEventListener) {

element.addEventListener(event, function (e) {

if (handler.call(this, e) === false) {

e.preventDefault();

}

});

}

} else if (element.attachEvent) {

element.attachEvent('on' + event, function (e) {

if (handler.call(element, e) === false) {

e.returnValue = false;

4 | Chapter 1: Event Handling

JavaScript does not do this automatically. Attempting to call .addEventListener

or .attachEvent on a list of elements will throw an error because it isn’t defined, and

calling the previously defined addEventListener function just won’t do anything, as

it won’t be able to find either method. In order to attach an event to multiple elements,

we have to loop through them:

var bars = document.getElementsByClassName('bar');

for (var i = 0; i < bars.length; i++) {

addEventListener(bars[i], 'click', callback);

}

document.getElementsByClassName returns a NodeList, not an array. One main dif-

ference between the two is that NodeLists update live, meaning that changes to the

DOM also change the NodeList:

var paragraphs = document.getElementsByTagName('p');

console.log(paragraphs.length); // 3

// Create a new paragraph element and append it to the body

console.log(paragraphs.length); // 4

Occasionally, this can result in an infinite loop in the page: say you have a function

that loops through all paragraph elements, and then copies them to the end of a page.

This will also copy them to the end of the NodeList, meaning that they will also be

copied to the end of the page again, and again, and again…

There are two ways to avoid this. The first is to cache the length of the NodeList:

var paragraphs = document.getElementsByTagName('p');

for (var i = 0, len = paragraphs.length; i < len; i++) {

document.body.appendChild(paragraphs[i].clone(true));

}

This means that if the original length of the NodeList were three, then it would only

clone three elements before stopping. The second approach would be to turn the

NodeList into an array:

var paragraphs = document.getElementsByTagName('p');

paragraphs = Array.prototype.slice.call(paragraphs);

for (var i = 0; i < paragraphs.length; i++) {

document.body.appendChild(paragraphs[i].clone(true));

}

We did this by calling the Array.slice method directly on the NodeList, causing it

to treat it like an array. We can call other array methods on the NodeList using the

same method; in the following example, we loop through all elements with a data-

number attribute and return an array containing all of them:

var elements = document.querySelectorAll('[data-number]');

var numbers = Array.prototype.map.call(elements, function (element) {

6 | Chapter 1: Event Handling

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