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HTML-id

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

index.html
<!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>

id

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​

index.html
<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>

id

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>

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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:

main.js
<script>
  function displayResult() {
    document.getElementById("myHeader").innerHTML =
      "Have a nice day!";
  }
</script>

id

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