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HTML id attribute

The HTML id property is used to provide an HTML element a unique identifier.

In an HTML page, you cannot have more than one element with the same id.

Using The id Attribute​

The id property of an HTML element gives a unique id. The id property value must be unique inside the HTML content.

The id property in a style sheet is used to point to a specific style declaration. JavaScript also uses it to access and alter the element with the specified id.

Write a hash character (#) followed by an id name in the syntax for id. The CSS properties are then defined within curly braces.

In the following example, we have a <h1> element with the id "myHeader." This <h1> element will be styled in the head section according to the #myHeader style definition:

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>
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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 numerous HTML elements on the same page, however an id name can only be used by one HTML element on the same 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">New Delhi</h2>
<p>New Delhi is the capital of India.</p>

<h2 class="city">Moscow</h2>
<p>Moscow is the capital of Russia.</p>

<h2 class="city">Tokyo</h2>
<p>Tokyo is the capital of Japan.</p>
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Using The id Attribute in JavaScript​

JavaScript may also utilize the id property to do various operations for that specific element.

The getElementById() function in JavaScript allows you to get an element with a given id:

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