React Hooks: useEffect() is called twice even if an empty array is used as an argument

December 15, 2022 By sanxbot00

When using the useEffect hook, the function passed as the first argument will be called every time the component renders, unless you specify an array of dependencies as the second argument.

If you want to prevent the useEffect function from being called more than once, you can pass an empty array as the second argument. This tells React that the effect does not depend on any values from the component’s props or state, so it should only be called once, when the component is initially rendered.

However, if the useEffect function is still being called multiple times even when passing an empty array as the second argument, it is possible that the effect itself is causing the component to re-render. This can happen if the effect changes the component’s state or props, or if it calls a function that does so.

To fix this issue, you can move the state update or function call outside of the useEffect hook, or you can use the useRef hook to avoid triggering a re-render.

Here is an example of using useRef to prevent the effect from being called multiple times:

import React, { useEffect, useRef } from 'react';

const MyComponent = () => {
  const firstRender = useRef(true);

  useEffect(() => {
    if (firstRender.current) {
      // Do something on initial render
      firstRender.current = false;
    } else {
      // Do something on subsequent renders
  }, []);

  // ...

In the above code, the useEffect function will only be called once on the initial render, because the useRef hook is used to track if it is the first render or not. This prevents the effect from causing the component to re-render, which would result in the useEffect function being called again.