What is memoization?

Memoization is an optimization technique in programming that stores the results of expensive function calls and returns the cached result when the same inputs occur again, rather than recomputing the function. In the context of React, memoization is used to prevent redundant re-renders of components.

In other words, you can say React is taking a snapshot of a component's output so when the component gets rendered again with the same props, React shows the saved snapshot instead of re-rendering everything from scratch. This saves time and makes the application run faster.

Wrap a functional component with React.memo to utilize it.

Example:

import React from "react";

const MyComponent = React.memo(({ prop1, prop2 }) => {
  // Component logic here 
  return (
    <div>
      <p>{prop1}</p>
      <p>{prop2}</p>
    </div>
  );
});

// Usage
<MyComponent prop1="Hello" prop2="world" />;

When To Use React.memo

So far, we have established that React.memo is an excellent optimization tool. However, it's crucial to recognize that it's not a one-size-fits-all solution. Understanding when to use it is essential to harnessing its benefits effectively. Here are some examples of situations where using React.memo makes sense:

• Parent Components with Static Props: In this case, when a parent component passes down static props to its child components, using React.memo on the child components can prevent them from re-rendering needlessly.

import React from "react";

const ChildComponent = React.memo(({ staticData }) => {
  console.log("Child component rendered");
  return <div>{staticData}</div>;
});

// Usage in parent component
function ParentComponent() {
  const staticData = "Static Data";

  return (
    <div>
      <ChildComponent staticData={staticData} />
    </div>
  );
}

export default ParentComponent;

• Large Lists and Grids: In a situation where components are used in lists or grids and each item has similar props, React.memo can come in handy. It will prevent the re-rendering of items that didn't change.

import React from "react";

const ListItem = React.memo(({ item }) => {
  console.log(`ListItem rendered for item: ${item}`);
  return <div>{item}</div>;
});

// Usage in a list component:
function List({ items }) {
  return (
    <div>
      {items.map((item) => (
        <ListItem key={item.id} item={item} />
      ))}
    </div>
  );
}

export default List;

• Optimizing Performance- Intensive Computations: When a component involves performance-intensive computations or data processing that doesn't depend on changing props or state, react.memo can save processing time by preventing recomputation on every render.

import React from "react";

const IntensiveComponent = React.memo(() => {
  const intensiveResult = computeIntensiveData();

  // Performance-intensive computations
  console.log('Intensive component rendered');

  return (
    <div>
      {intensiveResult}
    </div>
  );
});

• Components with Frequent Updates: Components that update frequently due to events like user interactions can benefit from React.memo. By memoizing these components, you can reduce the overhead of rendering.

import React, { useState } from "react";

const UpdatingComponent = React.memo(({ value }) => {
  console.log(`Updating component rendered with value: ${value}`);
});

function App() {
  const [count, setCount] = useState(0);

  const handleIncrement = () => {
    setCount(count + 1);
  };

  return (
    <div>
      <button onClick={handleIncrement}>Increment</button>
      <UpdatingComponent value={count} />
    </div>
  );
}

export default App;

• Memoization-Ready Data: If you're using memoized data from a state management library like Redux, React.memo can complement it by preventing unnecessary renders. Here's a simplified example using Redux:

import React from "react";
import { useSelector } from "react-redux";

const MemoizedComponent = React.memo(() => {
  const data = useSelector((state) => state.someMemoizedData);

  console.log('MemoizedComponent rendered');

  return (
    <div>
      {data}
    </div>
  );
});

export default MemoizedComponent;

Conclusion

In conclusion, remember, while React.memo is a helpful optimization tool, it's essential to use it judiciously. Not all components need to be memoized, and overusing them can lead to more complex code without significant performance gains.