What is the difference between id and class in CSS, and when should I use them?

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byAnton Shumikhin·Aug 30, 2024

Deploy id for a singular element on the page, symbolized with # in CSS. Settle on class to assemble elements with uniform styles, marked by .. IDs cater to uniqueness, classes cater to multiplicity.

Example:

<div id="main-header">/** This header is one of its kind! 😎 */</div>
<div class="button">/** We have a bunch of these! 👯‍♂️ */</div>
<div class="button">/** More buttons, more fun! */</div>

#main-header { font-size: 24px; /** Because size does matter! */ }
.button { background-color: green; /** Green is the new black. */ }

Mobilize #id for exclusivity, .class for uniformity.

Configuring individuality vs. uniformity

Both id and class perform distinct yet complementary roles in CSS:

IDs:
- Spike specificity for unique styles.
- Act as an anchor for JavaScript handling.
- Ensure unique occurrence per page, great for section headers or modals.
Classes:
- Champions of reusability and efficiency.
- Provide styling flexibility via multiple classes per element.
- Optimal for common styles and shared behaviors, like buttons or form inputs.

Notably, misapplication of id and class may lead to code maintainability complications. Stick to best practices, and your code shall thank you!

The specificity showdown

Sometimes, hyper-specificity rules the roost:

id might be the game-changer for critical elements, as in anchor navigation.
Using id in JavaScript dom manipulation offers pinpoint access; whereas classes foster bulk operations.

Caution, though! An id overdose can lead to convoluted dependencies, making future amendments a Herculean task.

Interface with libraries and performance matters

Framework interoperability can significantly nudge your choice:

With jQuery, class-based queries ensue, making classes the go-to for behavior.
When teaming up with React, class morphs into className, aligning smoothly with component architecture.

Performance too, can be a decisive factor:

Overused IDs can lead to heavier CSS files and lethargic style recalculations.
Classes keep the style sheet light and breezy, enabling cleaner, more readable code.

Enhancing accessibility and interaction with id and class

Discerningly leveraging id and class can enhance accessibility and interactions:

Lean on id to label interactive components with <label> for assistive technologies.
Utilize class for visual interaction cues such as hover states or transitions.