HtmlComparisonBeginner · 3 min read

Id vs Class in HTML: Key Differences and When to Use Each

In HTML, a id is a unique identifier for a single element, while a class can be shared by multiple elements. Use id for one specific element and class to group elements for styling or scripting.

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Quick Comparison

Here is a quick side-by-side comparison of id and class attributes in HTML:

Feature	`id`	`class`
Uniqueness	Must be unique on the page	Can be used on multiple elements
Purpose	Identify a single element	Group multiple elements
CSS Selector	Use `#id`	Use `.class`
JavaScript Access	Access with `getElementById`	Access with `getElementsByClassName` or `querySelectorAll`
Number per Element	One `id` per element	Multiple `class` names allowed per element
Specificity	`id` has higher CSS specificity	`class` has lower CSS specificity

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Key Differences

The id attribute is designed to uniquely identify one element on the page. This means no two elements should share the same id. It is often used for targeting a specific element in CSS or JavaScript. Because it is unique, CSS selectors using #id have higher specificity, so styles applied with an id override those with classes if there is a conflict.

On the other hand, the class attribute is meant to group multiple elements that share common styles or behavior. You can assign the same class to many elements, and an element can have multiple classes separated by spaces. This makes class very flexible for styling and scripting multiple elements at once.

In JavaScript, you access an element by id using document.getElementById(), which returns a single element. For classes, you use document.getElementsByClassName() or document.querySelectorAll(), which return collections of elements.

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Code Comparison

html

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Using id Example</title>
  <style>
    #unique-box {
      width: 150px;
      height: 150px;
      background-color: lightblue;
      text-align: center;
      line-height: 150px;
      font-weight: bold;
      margin: 20px auto;
      border: 2px solid blue;
    }
  </style>
</head>
<body>
  <div id="unique-box">ID Box</div>
</body>
</html>

Output

A single centered light blue box with the text 'ID Box' inside it.

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Class Equivalent

html

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Using class Example</title>
  <style>
    .colored-box {
      width: 150px;
      height: 150px;
      background-color: lightgreen;
      text-align: center;
      line-height: 150px;
      font-weight: bold;
      margin: 20px auto;
      border: 2px solid green;
    }
  </style>
</head>
<body>
  <div class="colored-box">Class Box 1</div>
  <div class="colored-box">Class Box 2</div>
</body>
</html>

Output

Two centered light green boxes stacked vertically, each with text 'Class Box 1' and 'Class Box 2' respectively.

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When to Use Which

Choose id when you need to identify one unique element on the page, such as a header, footer, or a specific button. This is useful for precise styling or JavaScript actions targeting that single element.

Choose class when you want to style or manipulate multiple elements in the same way, like buttons, cards, or sections that share common styles or behavior. Classes offer flexibility and reusability.

Remember, an element can have multiple classes but only one id. Avoid using the same id on multiple elements to keep your HTML valid and your scripts reliable.

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Key Takeaways

id is unique per page; class can be shared by many elements.

Use id for single elements needing unique styling or scripting.

Use class to group elements for shared styles or behavior.

id selectors have higher CSS specificity than class selectors.

An element can have multiple classes but only one id.