HTML - The id attribute
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>
Note: The id name is case sensitive!
Note: The id name must contain at least one character, cannot start with a number, and must not contain whitespaces (spaces, tabs, etc.).
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>
Tip: You can learn much more about CSS in our CSS Tutorial.
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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
Use the id attribute to manipulate text with JavaScript:
<script>
function displayResult() {
document.getElementById("myHeader").innerHTML = "Have a nice day!";
}
</script>
Tip: Study JavaScript in the HTML JavaScript chapter, or in our JavaScript Tutorial.
Chapter Summary
- The id attribute is used to specify 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 by CSS and JavaScript to style/select a specific element
- The value of the id attribute is case sensitive
- The id attribute is also used to create HTML bookmarks
- JavaScript can access an element with a specific id with the getElementById() method
HTML Exercises
Test Yourself With Exercises
Exercise:
Add the correct HTML attribute to make the H1 element red.
<!DOCTYPE html>
<html>
<head>
<style>
#myheader {color:red;}
</style>
</head>
<body>
<h1 >My Home Page</h1>
</body>
</html>
