What is the id attribute in html? Use of id attribute

tag respectively; then, these two values ​​cannot Used again in the id attribute of other tags.

The syntax of the id attribute:

<p ID="p1">测试文字</p>
<p id="p1">测试文字</p>
<p Id="p1">测试文字</p>
<p iD="p1">测试文字</p>

The above writing methods can be used. Let’s take a look at the effect of using css to add font color to #p1:

#p1{
color: red;
}

Rendering:

Rules for using the id attribute

The id attribute of html can be used anywhere in the document , but some rules must be followed:

1. The value of the id attribute must start with a letter (az or AZ) , for example:

<p id="p">测试文字</p>
<p id="A">测试文字</p>

Description: id attribute The value is case-sensitive

2. The subsequent characters can be letters, numbers (0-9), hyphens (-), and underscores (_)

<p id="pa">测试文字</p>
<p id="A1">测试文字</p>
<p id="p-a">测试文字</p>
<p id="A_1">测试文字</p>

3. Each id attribute value must be unique in the document

This makes it easier for us to use this id attribute value to determine the unique element of the Web site, and we can use css Or js to operate this unique element, for example: setting the element style, modifying the content contained in the element, etc.

Usage of id attribute

The id attribute is a very powerful attribute that can perform multiple operations for a Web page:

1. Style sheet selector (id selector):

This is a function of the ID attribute that most people are using. Because they are unique, when we style using the ID attribute, we ensure that only one item on the web page is styled. Example:

#p1{
color: red;
}

<p id="p1">测试文字</p>

Rendering:

2. Used in the named anchor point to link to:

Web browsers allow us to locate precise locations in web documents by pointing to the ID value at the end of the URL. We simply add the id value to the end of the page URL and prepend it with a pound sign (#). We can also link to these anchors on the page itself by adding a pound sign (#) and an ID name in the element's href attribute. Example:

<div class="demo">
	<ul>
		<li>
			<a href="#a1">标题1</a>
		</li>
		<li>
			<a href="#a2">标题2</a>
		</li>
		<li>
			<a href="#a3">标题3</a>
		</li>
	</ul>
	<div class="container">
		<div>
			<h3 id="a1">标题1</h3>
			<p>测试文字！测试文字！测试文字！测试文字！</p>
		</div>
		<div>
			<h3 id="a2">标题2</h3>
			<p>测试文字！测试文字！测试文字！测试文字！</p>
		</div>
		<div>
			<h3 id="a3">标题3</h3>
			<p>测试文字！测试文字！测试文字！测试文字！</p>
		</div>
	</div>
</div>

Rendering:

3. Use

in the script when we When you need to find an HTML element in Javascript, you can use the ID attribute to accurately find an element and set it. Example:

<p id="p1">测试文字！</p>

<script>
	document.getElementById("p1").innerHTML="PHP中文网!"
</script>

Rendering:

4. Other processing

The id attribute allows us to use any way to process web documents. For example, it can be used with PHP to extract HTML into a database, with the ID attribute identifying the field.

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