This content originally appeared on DEV Community and was authored by Geetika Bajpai
useMemo is a hook that allows you to memoize expensive calculations to avoid unnecessary re-computations on every render.
Explanation of the Code
This React component, MemoTutorial, demonstrates how to use the useMemo hook to optimize performance by memoizing the result of a function that computes the longest name from a list of comments fetched from an API. Let's break down the code step by step.
1. Imports:
- axios is used to make HTTP requests.
- useEffect, useState, and useMemo are hooks from React.
2. Component Definition:
The MemoTutorial function is the React component.
3. State Variables:
-
data: Holds the comments fetched from the API. -
toggle: A boolean used to trigger re-renders.
4. Fetching Data:
-
useEffectis used to fetch data from the API when the component mounts. - The empty dependency array ([]) ensures this effect runs only once.
5. Finding the Longest Name:
- This function iterates through the comments array to find and return the longest name.
6. Using useMemo:
- useMemo memoizes the result of findLongestName(data).
- The function findLongestName(data) is called only when toggle changes.
- If toggle remains unchanged, the previously computed result is returned without recomputing.
7. Rendering the Component:
- getLongestName is displayed in a div.
- A button toggles the toggle state.
- When toggle is true, "toggle" is displayed in an h1.
Why Use useMemo?
1. Performance Optimization:
- It helps prevent expensive calculations from being performed on every render.
- In this example, findLongestName can be computationally expensive if the list of comments is large.
2. Dependencies:
- The result of the memoized function (findLongestName) is recalculated only when the specified dependencies ([toggle]) change.
- If the dependencies do not change, React returns the memoized value from the previous render.
3. Example Context:
- Here, useMemo ensures findLongestName(data) is only recalculated when toggle changes.
- Even if the component re-renders due to changes in other state or props, the memoized result is reused, avoiding redundant computations.
This content originally appeared on DEV Community and was authored by Geetika Bajpai
Geetika Bajpai | Sciencx (2024-06-26T20:50:39+00:00) useMemo Hook. Retrieved from https://www.scien.cx/2024/06/26/usememo-hook/
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