As React applications grow, performance optimization becomes a necessity to avoid unnecessary renders and improve user experience. In this chapter, we will explore how to use React.memo and the useMemo hook to optimize components and expensive calculations in React applications.

react memo vs usememo

What is React.memo?

React.memo is a function that memoizes functional components. This means React will only re-render the component if the properties (props) change. It is especially useful in components that receive large amounts of data or those that render frequently.

Example of React.memo in Functional Components

In this example, we use React.memo to optimize a list component that displays items:

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Limitations of React.memo

Although React.memo optimizes performance by avoiding unnecessary renders, there are cases where it may not be useful:

• Referential props: If the properties change in reference but not in content (like a recreated array), the component will re-render.
• Comparison costs: In some cases, the comparison of the properties may be as costly as the rendering itself.

Optimizing Expensive Calculations with useMemo

The useMemo hook allows you to memoize the result of expensive calculations, executing the function only when a dependency changes. This is useful in cases where a calculation relies on props or states that change infrequently.

Basic Example of useMemo

In the following example, we use useMemo to memoize the result of an intensive calculation function:

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Combined Cases: React.memo and useMemo

In complex components that receive many props, React.memo and useMemo can be used in combination to optimize both the component rendering and internal calculations. This combination is particularly useful in applications that handle large volumes of data or lists.

Example of React.memo with useMemo

Here we show how React.memo and useMemo can work together in a component that calculates complex values for each item in a list:

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Best Practices When Using React.memo and useMemo

• Use in Heavy Components: Apply React.memo to large components or those that receive many props.
• Be Careful with Dependencies in useMemo: Ensure that useMemo dependencies are correctly defined to avoid reference errors.
• Measure the Impact: Use tools like React Profiler to identify if any performance gains are significant.

Conclusion

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React.memo and useMemo are powerful tools for optimizing component performance and calculations in React. In this chapter, we explored how and when to use these optimizers to avoid unnecessary renders and calculations. In the next chapter, we will dive into the use of Suspense for data fetching and handling asynchronous data loading.