JavaScript DOM编程艺术第四章 — JavaScript图片库案例研究

二森 2021-06-17 16:40:22
编程 javascript DOM 第四章 艺术


这一章通过JavaScript图片库案例,学习了一些DOM属性。

HTML代码

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>图片库</title>
<link rel="stylesheet" href="styles/layout.css" media="screen" />
</head>
<script type="text/javascript" src="scripts/showPic.js"></script>
<body>
<h1>Snapshots</h1>
<ul>
<li>
<a href='images/1.jpg' title="黄昏海边" onclick="showPic(this);
return false;">黄昏海边</a>
</li>
<li>
<a href='images/2.jpg' title="大漠孤烟直" onclick="showPic(this);
return false;">沙漠</a>
</li>
<li>
<a href='images/3.jpg' title="湖泊" onclick="showPic(this);
return false;">湖泊</a>
</li>
<li>
<a href='images/4.jpg' title="可爱熊熊" onclick="showPic(this);
return false;">可爱壁纸</a>
</li>
<li>
<a href='images/5.jpg' title="哆啦A梦" onclick="showPic(this);
return false;">哆啦A梦</a>
</li>
</ul>
<img id="placeholder" src="images/gallery.png" alt="my image gallery" />
<p id="description">Choose an image.</p>
</body>
</html>

几个DOM属性

1. childNodes属性

  • 用来获取任何一个元素的所有子元素
  • 使用方式:element.childNodes
  • 返回值:这个元素的所有子元素数组。包含所有类型的节点:元素节点、文本节点和属性节点。(实际上,文档里几乎每个东西都是一个节点,甚至连空格和换行符都是节点)

-- 示例:输出body元素的全体子元素

function countBodyChildren() {
let body_element = document.getElementsByTagName('body')[0];
console.log(body_element.childNodes);
}

-- 输出:
image

如图可见,body元素的子元素有9个,除了h1元素、ul元素、p元素、img元素四个外,还包括5个文本节点。

-- 文本节点示例:
image

2. nodeType属性

  • 获取每个节点的type(元素节点、文本节点还是属性节点)
    • 元素节点的nodeType属性值:1
    • 属性节点的nodeType属性值:2
    • 文本节点的nodeType属性值:3
  • 使用方式:node.nodeType

-- 示例

let body_element = document.getElementsByTagName('body')[0];
alert(body_element.nodeType);

-- 输出:1

3. nodeValue属性

  • 获取 or 设置节点的值
  • 获取节点的值使用方式:node.nodeValue
  • 设置节点的值使用方式:node.nodeValue = xxx
  • 注意,元素节点的nodeValue值是null。如果想获取p元素所包含的文本值,则需要获取元素所包含的文本值,则需要获取p元素的第一个子节点

-- 示例:输出 p元素的nodeValue 和 p的childNodes 以及 第一个子节点的nodeValue

function countBodyChildren() {
let description = document.getElementsById('description');
console.log(description.nodeValue);
console.log(description.childNodes);
console.log(description.childNodes[0].nodeValue);
}

--- 输出:
image

-- 示例:将p元素nodeValue值设置为'hello world'

function countBodyChildren() {
let description = document.getElementById('description');
description.childNodes[0].nodeValue = 'hello world';
console.log(description.childNodes[0].nodeValue);
}

--- 输出:
image

4. firstChild和lastChild属性

  • 指childNodes的第一个元素和最后一个元素,相当于简写,如下:
    • node.firstChild ——> node.childNodes[0]

    • node.lastChild ——> node.childNodes[node.childNodes.length - 1]

完整代码

1. HTML见上

2. JavaScript

function showPic(whichPic) {
let source = whichPic.getAttribute('href');
let placeholder = document.getElementById('placeholder');
placeholder.setAttribute('src', source);
let title = whichPic.getAttribute('title');
let description = document.getElementById('description');
description.firstChild.nodeValue = title;
}

3. CSS

body {
font-family: 'Helvetica', 'Arial', serif;
color: #333;
background-color: #ccc;
margin: 1em 10%;
}
h1 {
color: #333;
background-color: transparent;
}
a {
color: #c60;
background-color: transparent;
font-weight: bold;
text-decoration: none;
}
ul {
padding: 0;
}
li {
float: left;
padding: 1em;
list-style: none;
}
img {
width: 80%;
display: block;
clear: both;
}

效果:
image

本章其它知识点

改变属性的方法除了setAttribute外,还可以使用非DOM的方法,比如改变某个input的value属性,

  • 使用setAttribute:element.setAttribute('value', 'the new value')
  • 使用非DOM解决方案:element.value = 'the new value'

非DOM解决方案是在DOM出现之前使用的方式,并非所有的属性都可以用这种方式设置属性,因此建议使用setAttribute,setAttribute可以修改文档中的任何一个元素的任何一个属性。

版权声明
本文为[二森]所创,转载请带上原文链接,感谢
https://www.cnblogs.com/Ersonnnn/p/14893957.html

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