HTML 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
"fixhub" */
.fixhub {
background-color: tomato;
color: white;
padding: 10px;
}
</style>
<!-- An element with a unique id -->
<h1 id="myHeader">ID Elemet</h1>
<!-- Multiple elements with same class
-->
<h2 class="fixhub">heading</h2>
<p>Paragraph</p>
<h2 class="fixhub">heading</h2>
<p>Paragraph</p>
<h2 class="fixhub">heading</h2>
<p>paragrapsh</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
Use the id attribute to
manipulate text with JavaScript:
<script>
function displayResult() {
document.getElementById("myHeader").innerHTML = "Have
a nice day!";
}
</script>
Chapter Summary
- The
idattribute is used to specify a unique id for an HTML element - The
value of the
idattribute must be unique within the HTML document - The
idattribute is used by CSS and JavaScript to style/select a specific element - The
value of the
idattribute is case sensitive - The
idattribute is also used to create HTML bookmarks - JavaScript
can access an element with a specific id with the
getElementById()method
