React Answers

How to fix missing dependency warning when using useEffect React Hook?

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The “missing dependency” warning in React’s useEffect hook occurs when we use a variable or a function inside the effect without including it in the dependency array. This warning indicates that the effect may not have the most up-to-date values of the variables it relies on. To fix this warning, we need to add any missing dependencies to the dependency array.

Here’s how we can fix the missing dependency warning:

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

function ExampleComponent() {
  const [count, setCount] = useState(0);
  const [isMounted, setIsMounted] = useState(true);

  useEffect(() => {
    // Effect code that relies on `count`
    console.log('Count updated:', count);

    // Effect code that relies on `isMounted`
    console.log('Component mounted:', isMounted);

    // If we using any external function or variable, add them to the dependency array
    // For example, if we  are using a function `someFunction`, add it here:
    // someFunction();
  }, [count, isMounted]); // Add count and isMounted to the dependency array

  return (
      <p>Count: {count}</p>
      <button onClick={() => setCount(count + 1)}>Increment</button>

export default ExampleComponent;

In this example, I've added count and `isMounted` to the dependency array of the `useEffect` hook. Now, whenever count or `isMounted` changes, the effect will run with the latest values of those variables.

Ensure that we only include the variables or functions that are directly used inside the effect. Adding unnecessary dependencies can lead to unnecessary re-renders or unexpected behavior.

By John Au-Yeung

Web developer specializing in React, Vue, and front end development.

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