Ever since I started using TypeScript, I can't stop using it. Sometimes finding the correct type and where you should import it from can be a real headache. Especially when building a ReactJS application. This blog post is a great chance to publicly document my most used React TypeScript types. I focus on functional components and react hooks.
The structure of the article is that each paragraph is a standalone tip.

Blog / React Hooks Cheat Sheet 👨‍💻 By Adam Tuttle on. 2020-10-23 I just finished watching this excellent video series on Egghead.I found that it really simplified a lot of the hard parts of useEffect and also explained a few of the other hooks that I haven't taken the time to learn yet.

React 2020 Cheatsheet small.pdf - Free download as PDF File (.pdf), Text File (.txt) or read online for free. Scribd is the world's largest social reading and publishing site. Open navigation menu. Celebrities Cheat Sheet. Watch: Joe Biden Wins 2020 U.S. Election: Celebrities React. Hello sunshine, happy Monday. (drumroll) the 2020 election. While your eyes were glued on Nevada. So here we go with a practical cheat sheet for React Testing Library. The elements in the lists below allows us to select components or HTML elements and make assertion about them. I made this list for my own use but then I thought to put it nice in an article and so make it easy for me to find it quick when I need it but also available to.

To create a React TypeScript project, we can use Create React App:

There have been lots of talks about the right way to import React. This is the most updated way to do it:

The return type of a functional component is ReactElement

If you want to extend the props of a native HTML element, you can use the generic class HTMLAttributes. Let's say I want to create a new button:

Note that we use destructuring to forward the props to the button element.

The children prop is of type ReactNode.

React's events system uses its own types and not the native HTML events. Make sure to import the event from the react library. import { MouseEvent } from 'react'.

Pass the correct type to the useRef generic. If you want to create a ref to an input element:

The ref.current type will automatically be HTMLInputElement.

The same goes for useState.

If you provide an initial value in both cases, the type will be inferred implicitly.

When creating custom hooks make sure to explicitly set the returns type. Otherwise, TypeScript may infer incorrectly the types.

This is far from being a complete cheat sheet but rather documents the things I use the most. Check out this awesome cheat sheet for more information: https://github.com/typescript-cheatsheets/react.

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I just finished watching this excellent video series on Egghead. I found that it really simplified a lot of the hard parts of useEffect and also explained a few of the other hooks that I haven't taken the time to learn yet. I was so impressed by it that I was inspired to write down an even shorter version for later reference to help reinforce the lessons, and also to share with you. If any of this feels like there's not enough detail for you, I would highly encourage you to check out the videos on egghead, where Ryan goes into more detail and gives examples for each.

useState

I'm not going to cover useState because that's out of scope for what I want to accomplish here, but it is a pre-requisite for understanding what's below. If that one doesn't make sense to you already, you won't understand the rest of these.

useEffect

useEffect has three different usage modes, and is used to synchronize React with anything that React doesn't control; from the page title to making AJAX requests or dealing with device api's (like getUserMedia).

1. No 2nd argument: Executes on every render.

2. Array of variables as 2nd argument: Executes any time any of those variables change.

3. Empty array as 2nd argument: Executes only on FIRST render, and never again until page refresh.

In this case, I'm attaching an event listener to the window's resize event, and if I re-run that every time the component re-renders, I'll be attaching a new listener every time, effectively calling my listener potentially hundreds or thousands of times every time the event occurs.

If your effect creates something that needs to be cleaned up when the component is removed (like removing created event listeners), the effect should return a function that does that cleanup work, and React will run it only when the cleanup is needed. Since that's exactly what I did in the last code block above, let's fix it to be correct here:

useRef

Not just for persisting a reference to an input element!

useRef can be treated similarly to useState, except that it doesn't trigger a re-render. If your render function displays the ref value, the rendered content won't be updated when the ref is updated, but if something triggers a re-render then the latest value from the ref is available to the render function. You can use this to track data changes in a more performant way, as long as you don't need those changes to be re-rendered.

useMemo

Memoization is caching the results of a pure function, which can be helpful if that function requires intensive or long-running calculations. While implementing memoization is a simple and well understood pattern, useMemo combines that with the API of useEffect so that it only ever runs if the input values change.

useCallback

Reactjs Regex Cheat Sheet

Whereas useMemo returns a memoized value, useCallback returns a memoized function. When you want to be able to pass the memoized callback function around as a property, use useCallback instead. Via closure this helps you expose functionality without exposing internal state.

useLayoutEffect

useLayoutEffect is different from useEffect in that it runs before the DOM paints. This allows you to make changes that will affect what your app looks like (positioning elements, for example), without causing the screen to flash with a repaint because you moved something immediately after it was painted.

useContext

Contexts have been around for a while now as a useful way to work around prop drilling. useContext makes it simple to create and access contexts wherever you need them.

Creating and applying the provider:

Using properties of the context elsewhere:

React Js Cheatsheet

useReducer

This one is like a mashup of useState and Redux. You dispatch actions that are all handled by a single (composable if you want) reducer, to update a state object containing multiple values. Generally considered a best practice not to group values that aren't related. For example, groupe the state for inputs in a form.

React Cheat Sheet Pdf

useDebugValue

Lastly, useDebugValue allows you to highlight something in the React Dev Toolsfrom inside a custom hook. Think of it like console.log but better. When your debug value is large or complex, you can improve app performance by passing a 2nd argument to useDebugValue. The 2nd argument is a function and is used to format the value. This can be a performance benefit because the format function is only called if the value is inspected in the dev tools.

This shows up in the devtools as a key-value pair, and the key name is the name of your custom hook.

Wrapping Up

As I mentioned at the top, this was a heavily summarized version of what I learned from Ryan Harris' egghead course, React Hooks: Revisited. Thanks to Ryan for a fantastic quick video course and his simple and clear explanations!