How to call useEffect React Hook on a component mount and unmount

With pure function React Components you're not allowed to use lifecycle methods like componentDidMount or componentWillUnmount.

These can be replaced with proper use of useEffect hook introduced in React version 16.8.

Here is the code that will run exactly once when a component is mounted and exactly once when it's supposed to be unmounted:

import { useEffect } from "React";

const ExampleComponent = () => {
  useEffect(() => {
    // Here goes the code you wish to run on mount

    return () => {
      // Here goes the code you wish to run on unmount
    }
  }, []);

  ...
}

It's crucial to pass an empty array as the second argument of useEffect function call. If you omit it or pass dependencies inside of array it won't work as intended.