react-useunmount

The problem

When using a useEffect return function for handling component unmounting, state is not available.

The gif below showcases the problem, and that our custom useUnmount works. If you look at the console on component unmount, our custom hook contains the active state unlike the standard useEffect. You can reproduce this below example your self by following the instructions at the bottom of this page "Full Example".

What this package does

This package is a super simple and minimal hook for storing an array of dependencies within a ref, making the data available on unmount - which is the effect function passed in as the first parameter.

It accepts a function as the first parameter, which gets called on component unmount, and a dependency array as the second parameter which is stored and passed back to the unmount function. Fundamentally it:

• Creates a ref to store the required data in
• Initiates a useEffect for when the dependencies change, which updates the ref
• Initiates a useEffect for component unmount, which calls your unmount function with the dependency data passed back as the first argument

When might I need this?

If you have state data currently stored within context, state or a reducer and you need it available when the component unmounts.

If you don't need any of the above data on unmount, then you may only need a standard React useEffect return function:

useEffect(() => {
  return () => {
    console.log("This will be called when the component unmounts");
  };
}, []);

Install

npm install --save react-useunmount

or with yarn:

yarn add react-useunmount

The core code of this package is just 20 lines, so you may feel more comfortable copying the file dist/index.js into your own internal libraries. If you are using TypeScript, then you should copy src/index.tsx instead.

Usage

import * as React from "react";
 
import { useUnmount } from "react-useunmount";
 
const Example = () => {
  const [state, setState] = useState();
 
  useUnmount(
    // Destructure argument #1 into the same order as passed dependencies
    ([refState]) => {
      console.log("State now available via ref: ", refState);
    },
    [state]
  );
 
  return </>;
};

Full Example

Want to see the full working example showcasing how this works, and why a standard useEffect isn't enough? Clone this repository and:

cd example && yarn start

License

MIT © WazzaJB