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HTML id Attribute

Learn how to use the HTML id attribute to uniquely identify elements for CSS styling, JavaScript manipulation, and creating bookmarks for navigation.

The HTML id attribute is used to specify a unique id for an HTML element.

You cannot have more than one element with the same id in an HTML document.

Using The id Attribute

The id attribute specifies a unique id for an HTML element. The value of the id attribute must be unique within the HTML document.

The id attribute is used to point to a specific style declaration in a style sheet. It is also used by JavaScript to access and manipulate the element with the specific id.

The syntax for id is: write a hash character (#), followed by an id name. Then, define the CSS properties within curly braces .

In the following example we have an <h1> element that points to the id name "myHeader". This <h1> element will be styled according to the #myHeader style definition in the head section:

<!DOCTYPE html>
<html>
	<head>
		<style>
			  background-color: lightblue;
			  color: black;
			  padding: 40px;
			  text-align: center;
			} 
		</style>
	</head>
	<body>
		<h2>The id Attribute</h2>
		<p>Use CSS to style an element with the id "myHeader":</p>
		<h1 id="myHeader">My Header</h1>
	</body>
</html>

Output:

Id Example

Difference Between Class and ID

A class name can be used by multiple HTML elements, while an id name must only be used by one HTML element within the page:

<!DOCTYPE html>
<html>
	<head>
		<style>
			/* Style the element with the id "myHeader" */
			  background-color: lightblue;
			  color: black;
			  padding: 40px;
			  text-align: center;
			}

			/* Style all elements with the class name "city" */
			.city {
			  background-color: tomato;
			  color: white;
			  padding: 10px;
			} 
		</style>
	</head>
	<body>
		<!-- An element with a unique id -->
		<h1 id="myHeader">My Cities</h1>
		<!-- Multiple elements with same class -->
		<h2 class="city">London</h2>
		<h2 class="city">Paris</h2>
		<h2 class="city">Tokyo</h2>
	</body>
</html>

Output:

Class vs. Id example

HTML bookmarks are used to allow readers to jump to specific parts of a webpage.

Bookmarks can be useful if your page is very long.

To use a bookmark, you must first create it, and then add a link to it.

Then, when the link is clicked, the page will scroll to the location with the bookmark.

Example:

First, create a bookmark with the id attribute:

<h2 id="C4">Chapter 4</h2>

Then, add a link to the bookmark ("Jump to Chapter 4"), from within the same page:

<a href="#C4">Jump to Chapter 4</a>

Or, add a link to the bookmark ("Jump to Chapter 4"), from another page:

<a href="html_demo.html#C4">Jump to Chapter 4</a>

Using The id Attribute in JavaScript

The id attribute can also be used by JavaScript to perform some tasks for that specific element.

JavaScript can access an element with a specific id with the getElementById() method:

<!DOCTYPE html>
<html>
	<body>
		<h2>Using The id Attribute in JavaScript</h2>
		<p>JavaScript can access an element with a specified id by using the getElementById() method:</p>
		<h1 id="myHeader">Hello World!</h1>
		<button onclick="displayResult()">Change text</button>

		<script>
		function displayResult() {
		  document.getElementById("myHeader").innerHTML = "Have a nice day!";
		}
		</script>
	</body>
</html>
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