Run useEffect Only Once

React's useEffect hook function is often used in function components, and its functions are similar to componentDidMount , componentDidUpdate and componentWillUnmount methods in class components. useEffect will be executed when the component is rendered, which may be more times than you might think.

In a simple example, useEffect may only run once. But in complex applications, especially when props changes are involved, this is not guaranteed. The problem is that if you perform operations such as getting data from the API in useEffect , it can result in repeated fetching of data, which is both inefficient and unnecessary.

The solution lies in the second parameter of useEffect .

The second parameter is an array containing variables that the component needs to check to ensure that changes have occurred before re-rendering. You can put any props and state into here for checking.

Alternatively, you can pass in an empty array:

import React, { useEffect } from 'react';

function App() {
  useEffect(() => {
    // Execute only once, for example, get data from the API}, []);

  Return (
    <div>
      {/* Use the obtained data*/}
    </div>
  );
}

This will ensure that useEffect only runs once.

Documentation description:

If you use this optimization, make sure the array contains all the values ​​in the component scope that change over time and is used by useEffect (such as props and state). Otherwise, your code will reference an outdated value from a previous render.

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