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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>

The document HTML Classes & HTML Id | HTML for Junior Classes - Class 3 is a part of the Class 3 Course HTML for Junior Classes.
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