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:
Example
<!DOCTYPE html>
<html>
<head>
<style>
#myHeader {
background-color: lightblue;
color: black;
padding: 40px;
text-align: center;
}
</style>
</head>
<body>
<h1 id=”myHeader”>My Header</h1>
</body>
</html>
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:
Example
<style>
/* Style the element with the id “myHeader” */
#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>
<!– An element with a unique id –>
<h1 id=”myHeader”>My Cities</h1>
<!– Multiple elements with same class –>
<h2 class=”city”>London</h2>
<p>London is the capital of England.</p>
<h2 class=”city”>Paris</h2>
<p>Paris is the capital of France.</p>
<h2 class=”city”>Tokyo</h2>
<p>Tokyo is the capital of Japan.</p>
HTML Bookmarks with ID and Links
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:
Example
<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:
Example
<!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>
