What Are Class Components in React and Are They Still Relevant?

What Are Class Components in React and Are They Still Relevant?

Class components are how React was written before hooks. You do not write new code with them, but you will read them in older codebases and interview questions. Here is what they are and whether they still matter.

What Class Components Are

A class component is an ES6 class that extends React.Component. It holds state in this.state, updates it with this.setState, and uses lifecycle methods to run side effects at specific points in the component's life.

How They Differ From Functional Components

Functional components are functions that return JSX and use hooks for state and effects. Class components bundle state, effects, and the component into one class with this, which brings binding issues and more boilerplate.

Why They Were Replaced

Class components split related logic across separate lifecycle methods, the this keyword confused beginners and caused binding bugs, and reusable stateful logic was hard to share. Hooks solved all of these.

Are They Still Relevant?

For writing new code, no. For reading existing code, yes. Many production codebases still have class components, and interviewers still ask about lifecycle methods. You do not need to write them, but you should understand them.

What You Should Know About Them

Understand this.state and this.setState, the main lifecycle methods like componentDidMount and componentWillUnmount, and how to map them to hooks. That is enough to read legacy code and pass interviews.

The Takeaway

Class components are React's older syntax, replaced by functional components with hooks. You write functional; you read class. Understand state, the main lifecycle methods, and how they map to hooks, and you are covered.