document 对象_方法
document 对象是 HTML 文档的根对象，它提供了许多方法来访问和操作文档的内容。
1. document.write() 方法
document.write() 方法用于向文档中写入 HTML 代码。它可以用来创建文档的结构，添加文本、图像、链接等元素。
html
<!DOCTYPE html>
<html>
<head>
<title>Document Write Example</title>
</head>
<body>
<h1>Hello World!</h1>
<script>
document.write("<p>This is a paragraph.</p>");
</script>
</body>
</html>
输出结果：
html
<!DOCTYPE html>
<html>
<head>
<title>Document Write Example</title>
</head>
<body>
<h1>Hello World!</h1>
<p>This is a paragraph.</p>
</body>
</html>
2. ElementById() 方法
html
<!DOCTYPE html>
<html>
<head>
<title>Get Element by ID Example</title>
</head>
<body>
<h1 id="heading">Hello World!</h1>
<script>
var heading = ElementById("heading");
lor = "red";
</script>
</body>
</html>
输出结果：
html
<!DOCTYPE html>
<html>
<head>
<title>Get Element by ID Example</title>
</head>
<body>
<h1 id="heading" >Hello World!</h1>
</body>
</html>
3. ElementsByTagName() 方法
html
<!DOCTYPE html>
<html>
<head>
<title>Get Elements by Tag Name Example</title>
</head>
<body>
<h1>Hello World!</h1>
<p>This is a paragraph.</p>
<script>
var paragraphs = ElementsByTagName("p");
for (var i = 0; i < paragraphs.length; i++) {
paragraphs[i].lor = "blue";
}
</script>
</body>
</html>
输出结果：
html
<!DOCTYPE html>
<html>
<head>
<title>Get Elements by Tag Name Example</title>
queryselectorall用法</head>
<body>
<h1>Hello World!</h1>
<p >This is a paragraph.</p>
</body>
</html>
4. ElementsByClassName() 方法
html
<!DOCTYPE html>
<html>
<head>
<title>Get Elements by Class Name Example</title>
</head>
<body>
<h1 class="heading">Hello World!</h1>
<p class="paragraph">This is a paragraph.</p>
<script>
var headings = ElementsByClassName("heading");
for (var i = 0; i < headings.length; i++) {
headings[i].lor = "red";
}
var paragraphs = ElementsByClassName("paragraph");    for (var i = 0; i < paragraphs.length; i++) {
paragraphs[i].lor = "blue";
}
</script>
</body>
</html>
输出结果：
html
<!DOCTYPE html>
<html>
<head>
<title>Get Elements by Class Name Example</title>
</head>
<body>
<h1 class="heading" >Hello World!</h1>

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