An In-Depth Look at the Difference Between useMemo and useCallback

UseCallback is used to optimize the rendering behavior of your React function components, while useMemo is used to memorize expensive calculations to avoid having to recalculate them on every render. As a standard construction of hooks, those two solutions are not so different. Like with effect, a hook that manages the side-effects in functional components, argument callback comes first, and then an array of dependencies.

It’s more of a technical article with lots of details, so let’s cut to the chase!

As a standard construction of hooks, usMemo and useCallback are not so different:

• useMemo memorizes expensive calculations to avoid redoing them on every render.
• useCallback optimizes the rendering behavior of React function components.

We’re sure that for many of you, this is enough to understand the difference. But let’s look deeper into the topic, though.

“Hooks?” Understanding React Hooks

What are React Hooks?

React Hooks are functions that allow you to use React features without writing a class. Hooks were first introduced in React 16.8.

These tools offer a more direct and functional approach to React’s fundamental concepts, such as:

• state
• lifecycle
• context

They let you reuse stateful logic across components and simplify your code. You can eliminate the need for higher-order components and render props. 

Hooks provide a way to: 

• handle side effects
• manage state
• utilize context

All this improves the modularity and readability of React apps.

Types of Hooks

Different React hook types serve different purposes:

• useState lets you add state to functional components. It returns a stateful value and a function to update it.
• useEffect lets you perform side effects in function components, such as fetching data. React remembers the function you passed and calls it after the DOM updates.
• useContext lets you access context values directly within a functional component. This makes consuming context easier.

Other notable hooks are:

• useReducer
• useRef
• useLayoutEffect
• useImperativeHandle
• useDebugValue
• useId
• useDeferredValue
• useTransition
• useInsertionEffect
• useSyncExternalStore

These hooks serve more specialized purposes. They manage complex state logic, reference DOM elements, customize the instance value exposed to parent components, etc.

Introduction to useMemo and useCallbackIntroduction to useMemo vs useCallback React

In complex React applications, performance optimization is critical. It helps maintain responsive user interfaces. 

useMemo and useCallback are specifically designed to help with this by memorizing values and callbacks. 

Let us explain their respective purposes in more detail:

• useMemo.
  This one makes sure the function is only recomputed when one of its dependencies is changed. This is useful for expensive calculations or passing complex objects as props to child components. As a result of memorization, useMemo can significantly improve performance.

Here we have a code example:

jsx

const memorizedValue = useMemo(() => computeExpensiveValue(a, b), [a, b]);

• useCallback.
  This one memorizes callbacks. This process makes sure the same reference on callback is returned on every render unless its dependencies change. It’s useful when passing callbacks as props to child components to prevent them from re-rendering unnecessarily. useCallback maintains stable function references. This reduces the rendering overhead and improves the app’s performance.

We have a code example for it as well:

jsx

const memorizedCallback = useCallback(() => {

  doSomething(a, b);

}, [a, b]);

Together, useMemo and useCallback become a fire combination. With it, you can rest assured your app will run fast, even as it grows in complexity.

Next Level: useMemo Syntax and Usage

To use useMemo in a React component, you provide it with these two things:

• a function
• a dependency array

The result will be re-executed only if one of the dependencies changes. 

Here’s a code example of how you can use useMemo:

jsx

import React, { useMemo } from 'react';

const MyComponent = ({ a, b }) => {

  const memorizedValue = useMemo(() => {

    // Expensive calculation here

    return a + b;

  }, [a, b]);

  return <div>{memorizedValue}</div>;

};

In this example, memorizedValue will only be recalculated when either a or b changes. This optimizes the component’s performance. 

How?

It avoids unnecessary calculations on every render.

Next Level: React useCallback Syntax and Usage

To use useCallback in a React component, you provide it with these two things:

• a callback
• a dependency array
• The reference on the callback will be changed only if one of the dependencies changes. 

Here’s a code snippet on how you can use useCallback:

jsx

import React, { useCallback } from 'react';

const MyComponent = ({ a, b }) => {

  const memorizedCallback = useCallback(() => {

    // Some action here

    console.log(a, b);

  }, [a, b]);

  return <Button onClick={memorizedCallback}>Click me</Button>;

};

In this example, reference on the memorizedCallback will only be changed when either the a or b value changes.

And how does this improve the app’s performance? The button component doesn’t re-render unnecessarily.

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ProCoders Compares useCallback vs useMemo

Similarities

• Both useMemo and useCallback are used to optimize performance in React apps. They prevent unnecessary re-renders and recalculations. This makes the app run faster.
• Both hooks use a dependencies array. They do it to determine when the memorized value or function should be updated. The array lists variables. When they change, it triggers the recomputation of the memorized value or function.

Differences

• The primary difference between useMemo and useCallback is what they memorize.
  • useMemo memorizes values
  • useCallback memorizes functions
• useMemo is suitable when you have expensive calculations or derived values. You may want to avoid recalculating them on every render. Examples include:
  • Calculating filtered lists
  • Complex mathematical computations
• useCallback is a good choice when you need to pass stable callback references to child components. But we already covered that. The goal is to avoid unnecessary re-renders. Common use cases include:
  • Event handlers
  • Callback functions

Recommended: Advantages of Vue.js

Choosing Between useMemo and useCallback: Best Practices from ProCoders

Choosing between useMemo and useCallback isn’t just about knowing their definitions—it’s about understanding when and why to use them effectively. Here are some key considerations to help you decide.

Avoid Overusing Memorization with useMemo and useCallback

React is already optimized; unnecessary memorization can make code harder to read without offering real performance benefits. Before using useMemo or useCallback, consider whether the computation or function re-creation is actually slowing down your app.

Focus on Dependencies

Both hooks rely on dependency arrays. If dependencies change too often, memorization loses its effectiveness. Keep dependencies minimal to avoid unnecessary recalculations.

For example, a function depends on multiple variables, but only a few actually impact the result. Then, including extra dependencies forces React to recompute when it isn’t needed.

Be Mindful of Reference Equality

A common mistake with useCallback is creating new objects inside the memorized function, which negates its purpose. If a function generates a new object or array on every render, React will still treat it as a different reference. This will trigger re-renders in child components.

To prevent this, keep object creation outside of useCallback or use React’s functional updates when working with setState.

Skip Memorizing Primitive Values

Using useMemo for simple values like numbers or strings is unnecessary. Memorization helps with computationally expensive operations, not basic assignments.

For instance, memorizing a single number doesn’t improve performance—it only adds complexity. Instead of useMemo(() => 5, []), just use const count = 5.

Consider the Memory Impact

Memorization stores values in memory, which can introduce overhead if overused. If recomputing a value is cheap, it’s better to let it recalculate rather than persist it unnecessarily.

If an operation runs in milliseconds, memorization won’t provide noticeable gains. The best approach is to profile your application and optimize only when there’s measurable lag.

When to Skip Memorization

Memorization is not a requirement for every project. It is most useful when:

• There is a measurable performance issue, such as expensive calculations or large re-renders.
• A function is being passed as a prop to child components, causing unnecessary re-renders due to reference changes.
• The computation being memorized actually benefits from avoiding re-execution.

If these conditions aren’t met, skipping memorization will keep your code cleaner and easier to maintain.

Choosing between useMemo and useCallback depends on whether you’re optimizing a value or a function. If you need to store a computed value efficiently, useMemo is the right choice. If you need to maintain a stable function reference to prevent unnecessary re-renders, useCallback is more appropriate. The key is knowing when the trade-off is worth it.

An In-Depth Example

A useMemo is called using React source code. A useCallback is called by the user. 

Here is an example:

function memoUsed() {

  const _  = useMemo(() => {

    return ‘insert JSX here’

  })

  return _

}

function callbackUsed() {

  const _  = useCallback(() => {

    return ‘insert JSX here’

  })

  return _()

}

As you can see, useMemo can be easily imitated. Use a string returned in two slightly different ways. A variable of useMemo contains only the result of the return. This means everything in the body of the argument function is ignored. 

A variable of useCallback contains a function without execution. It simply uses a straight string, also known by the user as a return statement. This means these two approaches have the exact re-render count and deliver the same results.

When to Use useMemo in React

Expensive Calculations: If you have a component that performs heavy calculations, you can use useMemo.

jsx

const expensiveCalculation = (num) => {

  // Some expensive calculation

  return num * 2;

};

const MyComponent = ({ num }) => {

  const memorizedValue = useMemo(() => expensiveCalculation(num), [num]);

  return <div>{memorizedValue}</div>;

};

Referential Equality for Dependency Arrays: When passing objects or arrays as dependencies to other hooks (like useEffect or useCallback), useMemo can help maintain referential equality.

jsx

const MyComponent = ({ items }) => {

  const memorizedItems = useMemo(() => items, [items]);

  useEffect(() => {

    // This effect will only run when memorizedItems changes

  }, [memorizedItems]);

  return <div>{memorizedItems.length}</div>;

};

Optimizing Render Performance: When you have a list or table that gets re-rendered frequently due to parent component updates, useMemo can help memorize the list data to avoid costly re-renders.

jsx

const MyComponent = ({ data }) => {

  const memorizedData = useMemo(() => data, [data]);

  return (

    <ul>

      {memorizedData.map((item) => (

        <li key={item.id}>{item.name}</li>

      ))}

    </ul>

  );

};

When to Use useCallback in React

Event Handlers: When passing event handlers to child components, useCallback ensures the use of the same function instance.

jsx

const MyComponent = () => {

  const handleClick = useCallback(() => {

    console.log('Button clicked');

  }, []);

  return <Button onClick={handleClick}>Click Me</Button>;

};

Dependencies in useEffect: When a function is used inside a useEffect and has dependencies, useCallback makes sure the function reference remains the same.

jsx

const MyComponent = ({ userId }) => {

  const fetchData = useCallback(() => {

    // Fetch data for the user

  }, [userId]);

  useEffect(() => {

    fetchData();

  }, [fetchData]);

  return <div>Data fetched</div>;

};

Performance Optimization in Memorized Components: When using React.memo to prevent unnecessary re-renders of child components, useCallback ensures that props passed to the child don’t change unless necessary.

jsx

const MyButton = React.memo(({ onClick }) => (

  <button onClick={onClick}>Click Me</button>

));

const MyComponent = () => {

  const handleClick = useCallback(() => {

    console.log('Button clicked');

  }, []);

  return <MyButton onClick={handleClick} />;

};

Conclusion

useMemo and useCallback difference may seem elusive. They are both very useful hooks. They help optimize performance in React applications. This, in turn, impacts not just the quality of the app but its rating and popularity as well.

And this does what?

Right, increases revenue for the business behind the app. 

useMemo memorizes the result of expensive calculations.

useCallback memorizes callbacks to prevent unnecessary re-renders. 

Both hooks help in improving the smoothness and speed of your application when used correctly.

To achieve a high level of performance, you have to understand when and how to use useMemo and useCallback.

Avoid overusing them and correctly manage dependencies to prevent common pitfalls and misconceptions.

Experiment with useMemo and useCallback in your React projects to get the best performance benefits. Start with small optimizations and gradually incorporate these hooks where they provide the most value. But make sure not to overdo it.

You can read more on React optimizations in our blog.

And if you need help, ProCoders is always here to provide top developers for your project. Contact us, and let’s make your app as speedy and crisp as possible! We have over 120 developers and other specialists who can help you complete the project successfully!