HTML Classes & HTML Id | HTML for Junior Classes - Class 3 PDF Download
The HTML class attribute is used to specify a class for an HTML element.
Multiple HTML elements can share the same class.
Using The class Attribute
- The class attribute is often used to point to a class name in a style sheet. It can also be used by a JavaScript to access and manipulate elements with the specific class name.
- In the following example we have three <div> elements with a class attribute with the value of "city". All of the three <div> elements will be styled equally according to the .city style definition in the head section:
Example
<!DOCTYPE html>
<html>
<head>
<style>
.city {
background-color: tomato;
color: white;
border: 2px solid black;
margin: 20px;
padding: 20px;
}
</style>
</head>
<body>
<div class="city">
<h2>London</h2>
<p>London is the capital of England.</p>
</div>
<div class="city">
<h2>Paris</h2>
<p>Paris is the capital of France.</p>
</div>
<div class="city">
<h2>Tokyo</h2>
<p>Tokyo is the capital of Japan.</p>
</div>
</body>
</html>
In the following example we have two <span> elements with a class attribute with the value of "note". Both <span> elements will be styled equally according to the .note style definition in the head section:
Example
<!DOCTYPE html>
<html>
<head>
<style>
.note {
font-size: 120%;
color: red;
}
</style>
</head>
<body>
<h1>My <span class="note">Important</span> Heading</h1>
<p>This is some <span class="note">important</span> text.</p>
</body>
</html>
The Syntax For Class
To create a class; write a period (.) character, followed by a class name. Then, define the CSS properties within curly braces {}:
Example
Create a class named "city":
<!DOCTYPE html>
<html>
<head>
<style>
.city {
background-color: tomato;
color: white;
padding: 10px;
}
</style>
</head>
<body>
<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>
</body>
</html>
Multiple Classes
- HTML elements can belong to more than one class.
- To define multiple classes, separate the class names with a space, e.g. <div class="city main">. The element will be styled according to all the classes specified.
- In the following example, the first <h2> element belongs to both the city class and also to the main class, and will get the CSS styles from both of the classes:
Example
<h2 class="city main">London</h2>
<h2 class="city">Paris</h2>
<h2 class="city">Tokyo</h2>
Different Elements Can Share Same Class
Different HTML elements can point to the same class name.
In the following example, both <h2> and <p> points to the "city" class and will share the same style:
Example
<h2 class="city">Paris</h2>
<p class="city">Paris is the capital of France</p>
Use of The class Attribute in JavaScript
- The class name can also be used by JavaScript to perform certain tasks for specific elements.
- JavaScript can access elements with a specific class name with the getElementsByClassName() method:
Example
Click on a button to hide all elements with the class name "city":
<script>
function myFunction() {
var x = document.getElementsByClassName("city");
for (var i = 0; i < x.length; i++) {
x[i].style.display = "none";
}
}
</script>
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 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>
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>
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