UseMemo vs React.memo: What's the difference?

    Friday, May 24, 202411 min read184 views
    UseMemo vs React.memo: What's the difference?

    When we create React applications, ensuring they work smoothly is vital for keeping users satisfied. We want our apps to run faster, so we use two helpful tools called React.memo() and useMemo(). React.memo() helps us by remembering how our components were last shown to users. If a component gets the same information again, React.memo() saves time by not showing it again, which is like skipping a step to make things quicker.

    On the other hand, useMemo() helps us by remembering the results of some work we did. So, if we've already figured something out before, useMemo() reminds us of the answer without needing to do all the work again. Both of these tools are important for making sure our React apps run smoothly and quickly, keeping users happy while they use them.

    Table of Contents

    • What is React.memo() ?

    • What is useMemo() ?

    • Difference Between React.memo vs usememo

    • Conclusion

    What is React.memo()?


    React.memo() serves as a robust tool within the React framework, tailored specifically to enhance the performance of functional components. In the intricate landscape of developing React applications, where seamless user experiences are paramount, the optimization of component rendering becomes imperative, particularly in scenarios where the complexity of the application might lead to rendering bottlenecks.

    With React.memo(), developers can strategically minimize the incidence of unnecessary re-renders that could potentially impede the fluidity of user interactions. Unlike useMemo(), which primarily targets the optimization of component function call results, React.memo() hones in on refining the rendering process of components themselves.

    By implementing a mechanism akin to memory retention, React.memo() intelligently caches the output of a component's rendering process based on the specific props it receives. Consequently, when subsequent renders occur and the component is supplied with identical props as in prior renders, React.memo() adeptly identifies this consistency and abstains from re-rendering the component. This nuanced behavior effectively curtails the refresh cycles, ensuring that the component refreshes only when necessary, thereby fostering a smoother and more responsive user experience.

    Let's break down how React.memo() works and when to use it

    Performance Optimization

    React.memo() helps optimize performance by preventing unnecessary re-renders of components. When a component is wrapped with React.memo(), it compares the previous props with the new props passed to the component. If the props haven't changed, React.memo() prevents the component from re-rendering, saving valuable rendering time.

    Usage: To use React.memo()

    you simply wrap your functional component with it. For example:

    import React from 'react';
    const MyComponent = React.memo((props) => {
        // Component logic here
    export default MyComponent;

    Let's consider a scenario where we have a parent component rendering multiple child components. If the parent component's state changes but the props passed to the child components remain the same, without React.memo(), all child components would re-render unnecessarily. However, by wrapping the child components with React.memo(), we can prevent these unnecessary re-renders, thus optimizing performance.

    Custom Comparison Function

    React.memo() also allows us to provide a custom comparison function as the second argument, where we can specify which props to compare for memoization. This is helpful when we want to customize how React.memo() determines whether a component should re-render or not.

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    What is useMemo()?

    useMemo() is another essential tool in React for optimizing performance, particularly in functional components. While React.memo() focuses on preventing unnecessary re-renders of components, useMemo() targets the optimization of expensive function calls within a component.

    Performance Optimization

    The primary purpose of useMemo() is to optimize performance by memoizing the result of a function call. When a component re-renders, useMemo() ensures that expensive calculations within the component are only performed when necessary. It achieves this by caching the result of the function call and returning the cached result when the inputs to the function remain the same.

    To utilize useMemo(), we wrap our expensive function inside it, along with a dependency array that specifies the inputs to the function. For example:

    import React, { useMemo } from 'react';
    const MyComponent = ({ data }) => {
        const expensiveCalculation = useMemo(() => {
            // Expensive calculation logic using data
            return result;
        }, [data]); // Dependency array
        return (
                {/* Render using the result of the expensive calculation */}
    export default MyComponent;

    Suppose we have a parent component passing data to a child component, triggering a re-render of the child component each time the data changes. Without useMemo(), the expensive calculation inside the child component would be re-executed on every render, even if the data remains the same. However, by wrapping the calculation with useMemo() and specifying the data as a dependency, we ensure that the calculation is only performed when the data changes, optimizing performance.

    Custom Comparison Function

    Similar to React.memo(), useMemo() also allows the use of a custom comparison function as the second argument. This function determines whether the cached result should be recalculated based on the previous value and the current value of the dependency.

    Difference Between react.memo vs usememo

    React.memo() is primarily used to optimize the rendering process of components. It memorizes the output of a component's rendering based on its props. When a component re-renders with the same props, React.memo() prevents unnecessary re-renders by returning the cached result, thus reducing the number of times the component refreshes.

    useMemo(), on the other hand, focuses on optimizing the performance of expensive function calls within a component. It memoizes the result of a function execution and returns the cached result when the inputs to the function remain the same, thereby preventing redundant calculations and improving performance.

    React.memo() is commonly applied to functional components, especially those receiving props from parent components. By wrapping a component with React.memo(), unnecessary re-renders are minimized, leading to better performance, particularly in scenarios where the parent component frequently updates but the props passed to the child component remain unchanged.

    useMemo() is typically used within functional components where expensive computations are performed based on certain inputs (usually props or state). By wrapping these computations with useMemo() and specifying the dependencies (inputs), we ensure that the computations are only recalculated when necessary, thus optimizing performance by avoiding redundant calculations.

    React.memo() relies on changes in props to determine whether a React component should re-render. It compares the previous props with the new props to decide whether to re-render the component.

    useMemo() depends on changes in specified dependencies (usually an array of inputs) to decide whether to recalculate the memoized component value. It re-executes the provided function only when the dependencies change, preventing unnecessary recalculations.

    HOC Wrapping: With HOCs, a component visually wraps with additional functionality by creating a new wrapper component that encloses the original one. This wrapping is typically done outside the component definition, which may lead to a higher level of abstraction.

    Hook Invocation
    Hooks are invoked directly inside the functional component body, enabling a more concise and intuitive way of managing state, effects, context, etc. This approach allows for more granular control over component logic and encourages better encapsulation.


    In conclusion, both React.memo() and useMemo() are crucial for optimizing performance in React applications. React.memo() helps minimize unnecessary component renders based on prop changes, while useMemo() optimizes expensive computations by memoizing results based on specified dependencies. By leveraging these tools appropriately, developers can significantly enhance the efficiency and responsiveness of their applications, ensuring smoother user experiences. However, it's essential to use them judiciously and understand their differences to address performance bottlenecks in React components effectively.


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