The Real Difference Between useMemo and memo in React

React, the popular JavaScript library for building user interfaces, provides a suite of tools and techniques to optimize the performance of your applications. Among them, useMemo and memo are two commonly used techniques to prevent unnecessary re-rendering of components. Despite their similar goals, they differ significantly in terms of their implementation and use cases. In this article, we'll dissect the real differences between useMemo and memo in React.

React.memo: What is it?

React provides React.memo, a higher-order component (HOC) that lets us optimize functional components. It functions by memoizing the render result of the component, so it won't re-render if the component gets the same props as previously. By minimizing pointless re-renders, this can greatly enhance our application's performance. We only need to wrap React.memo around our functional component in order to use it:

import React from "react";

const MyComponent = React.memo((props) => {
  // component logic here
});

export default MyComponent;        

A crucial point to remember is that React.memo compares the props only superficially by default. This implies that the component will re-render if the props object or any key within it has a different reference. You can give React.memo a custom comparison function as its second argument if you require a more complex comparison.

React useMemo: What is it?

React offers a hook called useMemo that lets us memoize costly calculations inside of our functional components. Its arguments are a dependency array and a callback function. Only in the event that any of the dependencies in the array have changed is the callback method re-executed.

Here's an example of how to use useMemo:

import React, { useMemo } from "react";
const MyComponent = () => {
  const expensiveValue = useMemo(() => {
    // compute the expensive value here
    return computeExpensiveValue(someDependency);
  }, [someDependency]);
  // component logic here
};        

Here are some more details about memo and useMemo:

• memo: relies on the component's props to determine whether it needs to re-render. It performs a shallow comparison by default, but allows for a custom comparison function if needed.
• useMemo: explicitly specifies its dependencies as a second argument in the form of an array.
• memo: caches a component's output based on its props.
• useMemo: caches a value based on its dependencies.
• memo: is used when you find an existing component that is expensive to render, and you don't have the option to optimize it internally.
• useMemo: is for internally optimizing a component by saving the return value of an expensive function call.

Conclusion

To sum up, React offers two effective utilities called React.memo and useMemo that help us maximize the efficiency of our apps. Making the best optimization choices requires an understanding of their variations and use cases.If you want to avoid having functional components render again when they frequently receive the same props, use React.memo. It can greatly enhance your application's performance by obviating expensive calculations.However, if you wish to memoize costly computations or calculations inside a functional component, useMemo. It enables you to prevent needless recalculations in the event that the dependencies remain unchanged.