When you work with React, one of the most important things to understand is its rendering lifecycle. Knowing how and when components render and re-render is key to writing applications that are not only correct but also performant and scalable.

Let’s break this down.

1. The React Rendering Lifecycle

At a high level, React components go through three main stages:

1. Initial Render
   • When a component is mounted for the first time, React builds the UI from scratch.
   • It reconciles the component’s JSX with the DOM and commits it to the screen.
2. Re-render (Updates)
   • A component re-renders when its state or props change.
   • React uses its Virtual DOM diffing algorithm to figure out what changed and updates only the necessary parts of the real DOM.
3. Unmount
   • When a component is removed, React cleans up resources like event listeners or effects to free memory.

2. Why Do Re-renders Matter?

Re-renders are natural they’re how React stays reactive.
But unnecessary re-renders can lead to:

• Slow UIs (laggy scrolling, delayed responses).
• Wasted resources (CPU cycles for DOM diffing and painting).
• Lower scalability (especially in apps with hundreds of components).

In short: Re-renders are good when needed, costly when excessive.

3. Common Causes of Excessive Re-renders

• Passing new object/array references as props (e.g., props={{}} in JSX).
• Unnecessary state updates (calling setState with the same value).
• Re-render chains where a parent update triggers child updates.
• Inline functions inside JSX that recreate on every render.

4. Optimizing React Re-renders

Here are practical strategies:

4.1 Memoization of Components

Use React.memo to prevent child components from re-rendering unless their props change.

const Child = React.memo(({ value }) => {
console.log("Rendered");
return <div>{value}</div>;
});

4.2 Stabilizing Functions with useCallback

Inline functions re-create on every render. Use useCallback to memoize them.

const handleClick = useCallback(() => {
console.log("Clicked");
}, []);

4.3 Avoid Unnecessary State

Not everything belongs in useState. Derive values from props or compute them directly when possible.

4.4 Memoizing Expensive Computations with useMemo

const sortedList = useMemo(() => expensiveSort(data), [data]);


4.5 Split Large Components

Break down complex components so React re-renders only the parts that need updating.

4.6 Virtualization for Large Lists

For thousands of items, use libraries like react-window or react-virtualized to render only what’s visible.

5. Mental Model for Re-renders

Think of React rendering like this:

• State/Props change → React re-renders the component.
• Virtual DOM diffing → Finds changes.
• DOM update → Applies only what’s necessary.

Your job as a developer?
👉 Minimize how often and how much React needs to re-render.

Conclusion

React’s rendering lifecycle is designed for efficiency, but careless coding can still lead to unnecessary re-renders. By memoizing, stabilizing references, deriving state smartly, and splitting components, you can keep your apps fast and scalable.

The golden rule: Don’t prematurely optimize every render. Measure with tools like React DevTools Profiler, identify real bottlenecks, and then apply these strategies.
Happy Coding!