Premise

I've created a simple counter in React that increases and decreases a number, using the useState hook in React to pass down props to the buttons. I wanted to create a hook that showed the previous total to the user

It uses useRef() to store the current value. This is then placed inside a variable. The useRef hook returns an object with one property (current) You can read more about useRef herehttps://reactjs.org/docs/hooks-reference.html#useref

usePreviousTotal

I've also used a useEffect hook as I'm reaching inside the DOM to grab the current value, this is stored in the dependancy array as I only want to render this when that value changes. You can read more about useEffect herehttps://reactjs.org/docs/hooks-effect.html

Now all that is left is to import the hook into the app.

And that's it. Look more at the React docs for more information.