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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>
<h2>The id Attribute</h2>
<p>Use CSS to style an element with the id “myHeader”:</p>
<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
<!DOCTYPE html>
<html>
<head>
<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>
</head>
<body>
<h2>Difference Between Class and ID</h2>
<p>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:</p>
<!– An element with a unique id –>
<h1 id=”myHeader”>My Cities</h1>
<!– Multiple elements with same class –>
<h2>London</h2>
<p>London is the capital of England.</p>
<h2>Paris</h2>
<p>Paris is the capital of France.</p>
<h2>Tokyo</h2>
<p>Tokyo is the capital of Japan.</p>
</body>
</html>
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
<!DOCTYPE html>
<html>
<body>
<p><a href=”#C4″>Jump to Chapter 4</a></p>
<p><a href=”#C10″>Jump to Chapter 10</a></p>
<h2>Chapter 1</h2>
<p>This chapter explains ba bla bla</p>
<h2>Chapter 2</h2>
<p>This chapter explains ba bla bla</p>
<h2>Chapter 3</h2>
<p>This chapter explains ba bla bla</p>
<h2 id=”C4″>Chapter 4</h2>
<p>This chapter explains ba bla bla</p>
<h2>Chapter 5</h2>
<p>This chapter explains ba bla bla</p>
<h2>Chapter 6</h2>
<p>This chapter explains ba bla bla</p>
<h2>Chapter 7</h2>
<p>This chapter explains ba bla bla</p>
<h2>Chapter 8</h2>
<p>This chapter explains ba bla bla</p>
<h2>Chapter 9</h2>
<p>This chapter explains ba bla bla</p>
<h2 id=”C10″>Chapter 10</h2>
<p>This chapter explains ba bla bla</p>
<h2>Chapter 11</h2>
<p>This chapter explains ba bla bla</p>
<h2>Chapter 12</h2>
<p>This chapter explains ba bla bla</p>
<h2>Chapter 13</h2>
<p>This chapter explains ba bla bla</p>
<h2>Chapter 14</h2>
<p>This chapter explains ba bla bla</p>
<h2>Chapter 15</h2>
<p>This chapter explains ba bla bla</p>
<h2>Chapter 16</h2>
<p>This chapter explains ba bla bla</p>
<h2>Chapter 17</h2>
<p>This chapter explains ba bla bla</p>
<h2>Chapter 18</h2>
<p>This chapter explains ba bla bla</p>
<h2>Chapter 19</h2>
<p>This chapter explains ba bla bla</p>
<h2>Chapter 20</h2>
<p>This chapter explains ba bla bla</p>
<h2>Chapter 21</h2>
<p>This chapter explains ba bla bla</p>
<h2>Chapter 22</h2>
<p>This chapter explains ba bla bla</p>
<h2>Chapter 23</h2>
<p>This chapter explains ba bla bla</p>
</body>
</html>
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:
<!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>
-
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
- The
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>