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# React+TypeScript Cheatsheets
Cheatsheets for experienced React developers getting started with TypeScript
---
<a href="https://github.com/typescript-cheatsheets/react/issues/81">
<img
height="90"
width="90"
alt="react + ts logo"
src="https://user-images.githubusercontent.com/84442212/194379444-02e5ec69-5e6c-4100-bd7a-c31d628af29c.png"
align="left"
/>
</a>
[**Web docs**](https://react-typescript-cheatsheet.netlify.app/docs/basic/setup) |
[**Español**](https://github.com/typescript-cheatsheets/react-typescript-cheatsheet-es) |
[**Português**](https://github.com/typescript-cheatsheets/react-pt) |
[Contribute!](https://github.com/typescript-cheatsheets/react/blob/main/CONTRIBUTING.md) |
[Ask!](https://github.com/typescript-cheatsheets/react/issues/new/choose)
:wave: This repo is maintained by [@swyx](https://twitter.com/swyx), [@eps1lon](https://twitter.com/sebsilbermann) and [@filiptammergard](https://twitter.com/tammergard). We're so happy you want to try out TypeScript with React! If you see anything wrong or missing, please [file an issue](https://github.com/typescript-cheatsheets/react/issues/new/choose)! :+1:
---
[](/CONTRIBUTORS.md) | [](https://discord.gg/wTGS5z9) | [](http://twitter.com/home?status=Awesome%20%40Reactjs%20%2B%20%40TypeScript%20cheatsheet%20by%20%40ferdaber%2C%20%40sebsilbermann%2C%20%40swyx%20%26%20others!%20https%3A%2F%2Fgithub.com%2Ftypescript-cheatsheets%2Freact)
## All React + TypeScript Cheatsheets
- [The Basic Cheatsheet](https://react-typescript-cheatsheet.netlify.app/docs/basic/setup) is focused on helping React devs just start using TS in React **apps**
- Focus on opinionated best practices, copy+pastable examples.
- Explains some basic TS types usage and setup along the way.
- Answers the most Frequently Asked Questions.
- Does not cover generic type logic in detail. Instead we prefer to teach simple troubleshooting techniques for newbies.
- The goal is to get effective with TS without learning _too much_ TS.
- [The Advanced Cheatsheet](https://react-typescript-cheatsheet.netlify.app/docs/advanced) helps show and explain advanced usage of generic types for people writing reusable type utilities/functions/render prop/higher order components and TS+React **libraries**.
- It also has miscellaneous tips and tricks for pro users.
- Advice for contributing to DefinitelyTyped.
- The goal is to take _full advantage_ of TypeScript.
- [The Migrating Cheatsheet](https://react-typescript-cheatsheet.netlify.app/docs/migration) helps collate advice for incrementally migrating large codebases from JS or Flow, **from people who have done it**.
- We do not try to convince people to switch, only to help people who have already decided.
- ⚠️This is a new cheatsheet, all assistance is welcome.
- [The HOC Cheatsheet](https://react-typescript-cheatsheet.netlify.app/docs/hoc)) specifically teaches people to write HOCs with examples.
- Familiarity with [Generics](https://www.typescriptlang.org/docs/handbook/2/generics.html) is necessary.
- ⚠️This is the newest cheatsheet, all assistance is welcome.
---
## Basic Cheatsheet
### Basic Cheatsheet Table of Contents
<details>
<summary><b>Expand Table of Contents</b></summary>
- [Section 1: Setup TypeScript with React](#section-1-setup-typescript-with-react)
<!--START-SECTION:setup-toc-->
- [Prerequisites](#prerequisites)
- [React and TypeScript starter kits](#react-and-typescript-starter-kits)
- [Try React and TypeScript online](#try-react-and-typescript-online)<!--END-SECTION:setup-toc-->
- [Section 2: Getting Started](#section-2-getting-started)
- [Function Components](#function-components)
- [Hooks](#hooks)
- [useState](#usestate)
- [useReducer](#usereducer)
- [useEffect / useLayoutEffect](#useeffect--uselayouteffect)
- [useRef](#useref)
- [Option 1: DOM element ref](#option-1-dom-element-ref)
- [Option 2: Mutable value ref](#option-2-mutable-value-ref)
- [See also](#see-also)
- [useImperativeHandle](#useimperativehandle)
- [Custom Hooks](#custom-hooks)
- [More Hooks + TypeScript reading:](#more-hooks--typescript-reading)
- [Example React Hooks + TypeScript Libraries:](#example-react-hooks--typescript-libraries)
- [Class Components](#class-components)
- [Typing getDerivedStateFromProps](#typing-getderivedstatefromprops)
- [You May Not Need `defaultProps`](#you-may-not-need-defaultprops)
- [Typing `defaultProps`](#typing-defaultprops)
- [Consuming Props of a Component with defaultProps](#consuming-props-of-a-component-with-defaultprops)
- [Problem Statement](#problem-statement)
- [Solution](#solution)
- [Misc Discussions and Knowledge](#misc-discussions-and-knowledge)
- [Typing Component Props](#typing-component-props)
- [Basic Prop Types Examples](#basic-prop-types-examples)
- [Useful React Prop Type Examples](#useful-react-prop-type-examples)
- [Types or Interfaces?](#types-or-interfaces)
- [TL;DR](#tldr)
- [More Advice](#more-advice)
- [Useful table for Types vs Interfaces](#useful-table-for-types-vs-interfaces)
- [getDerivedStateFromProps](#getderivedstatefromprops)
- [Forms and Events](#forms-and-events)
- [List of event types](#list-of-event-types)
- [Context](#context)
- [Basic Example](#basic-example)
- [Extended Example](#extended-example)
- [forwardRef/createRef](#forwardrefcreateref)
- [Generic forwardRefs](#generic-forwardrefs)
- [Option 1 - Wrapper component](#option-1---wrapper-component)
- [Option 2 - Redeclare forwardRef](#option-2---redeclare-forwardref)
- [More Info](#more-info)
- [Portals](#portals)
- [Error Boundaries](#error-boundaries)
- [Option 1: Using react-error-boundary](#option-1-using-react-error-boundary)
- [Options 2: Writing your custom error boundary component](#options-2-writing-your-custom-error-boundary-component)
- [Concurrent React/React Suspense](#concurrent-reactreact-suspense)
- [Troubleshooting Handbook: Types](#troubleshooting-handbook-types)
<!--START-SECTION:types-toc-->
- [Union Types and Type Guarding](#union-types-and-type-guarding)
- [Optional Types](#optional-types)
- [Enum Types](#enum-types)
- [Type Assertion](#type-assertion)
- [Simulating Nominal Types](#simulating-nominal-types)
- [Intersection Types](#intersection-types)
- [Union Types](#union-types)
- [Overloading Function Types](#overloading-function-types)
- [Using Inferred Types](#using-inferred-types)
- [Using Partial Types](#using-partial-types)
- [The Types I need weren't exported!](#the-types-i-need-werent-exported)
- [The Types I need don't exist!](#the-types-i-need-dont-exist)
- [Slapping `any` on everything](#slapping-any-on-everything)
- [Autogenerate types](#autogenerate-types)
- [Typing Exported Hooks](#typing-exported-hooks)
- [Typing Exported Components](#typing-exported-components)
- [Frequent Known Problems with TypeScript](#frequent-known-problems-with-typescript)
- [TypeScript doesn't narrow after an object element null check](#typescript-doesnt-narrow-after-an-object-element-null-check)
- [TypeScript doesn't let you restrict the type of children](#typescript-doesnt-let-you-restrict-the-type-of-children)<!--END-SECTION:types-toc-->
- [Troubleshooting Handbook: Operators](#troubleshooting-handbook-operators)
- [Troubleshooting Handbook: Utilities](#troubleshooting-handbook-utilities)
- [Troubleshooting Handbook: tsconfig.json](#troubleshooting-handbook-tsconfigjson)
- [Troubleshooting Handbook: Fixing bugs in official typings](#troubleshooting-handbook-fixing-bugs-in-official-typings)
- [Troubleshooting Handbook: Globals, Images and other non-TS files](#troubleshooting-handbook-globals-images-and-other-non-ts-files)
- [Editor Tooling and Integration](#editor-tooling-and-integration)
- [Linting](#linting)
- [Other React + TypeScript resources](#other-react--typescript-resources)
- [Recommended React + TypeScript talks](#recommended-react--typescript-talks)
- [Time to Really Learn TypeScript](#time-to-really-learn-typescript)
- [Example App](#example-app)
</details>
<!--START-SECTION:setup-->
### Section 1: Setup
#### Prerequisites
You can use this cheatsheet for reference at any skill level, but basic understanding of React and TypeScript is assumed. Here is a list of prerequisites:
- Basic understanding of [React](https://react.dev/).
- Familiarity with [TypeScript Basics](https://www.typescriptlang.org/docs/handbook/2/basic-types.html) and [Everyday Types](https://www.typescriptlang.org/docs/handbook/2/everyday-types.html).
In the cheatsheet we assume you are using the latest versions of React and TypeScript.
#### React and TypeScript starter kits
React has documentation for [how to start a new React project](https://react.dev/learn/start-a-new-react-project) with some of the most popular frameworks. Here's how to start them with TypeScript:
- [Next.js](https://nextjs.org/docs/basic-features/typescript): `npx create-next-app@latest --ts`
- [Remix](https://remix.run/docs/tutorials/blog): `npx create-remix@latest`
- [Gatsby](https://www.gatsbyjs.com/docs/how-to/custom-configuration/typescript/): `npm init gatsby --ts`
- [Expo](https://docs.expo.dev/guides/typescript/): `npx create-expo-app -t with-typescript`
#### Try React and TypeScript online
There are some tools that let you run React and TypeScript online, which can be helpful for debugging or making sharable reproductions.
- [TypeScript playground](https://www.typescriptlang.org/play?target=8&jsx=4#code/JYWwDg9gTgLgBAbzgVwM4FMDKMCGN0A0KGAogGZnoDG8AvnGVBCHAORTo42sDcAsAChB6AB6RYcKhAB2qeAGEIyafihwAvHAAUASg0A+RILiSZcuAG0pymEQwxFNgLobiWXPi0AGHfyECTNHRyShotXQMjAJM4ABMIKmQQdBUAOhhgGAAbdFcAAwBNJUks4CoAa3RYuAASBGsVegzk1Dy-E1pfQWM4DhhkKGltHpMAHn0RmNGwfSLkErLK6vqlRrhm9FRRgHoZybGAI2QYGBk4GXlSivUECPVDe0cVLQb4AGo4AEYdWgnomJil0WcGS+zgOyOJxkfwBOxhcC6AlogiAA)
- [StackBlitz](https://stackblitz.com/fork/react-ts)
- [CodeSandbox](https://ts.react.new/)
<!--END-SECTION:setup-->
### Section 2: Getting Started
<!--START-SECTION:function-components-->
#### Function Components
These can be written as normal functions that take a `props` argument and return a JSX element.
```tsx
// Declaring type of props - see "Typing Component Props" for more examples
type AppProps = {
message: string;
}; /* use `interface` if exporting so that consumers can extend */
// Easiest way to declare a Function Component; return type is inferred.
const App = ({ message }: AppProps) => <div>{message}</div>;
// you can choose annotate the return type so an error is raised if you accidentally return some other type
const App = ({ message }: AppProps): React.JSX.Element => <div>{message}</div>;
// you can also inline the type declaration; eliminates naming the prop types, but looks repetitive
const App = ({ message }: { message: string }) => <div>{message}</div>;
// Alternatively, you can use `React.FunctionComponent` (or `React.FC`), if you prefer.
// With latest React types and TypeScript 5.1. it's mostly a stylistic choice, otherwise discouraged.
const App: React.FunctionComponent<{ message: string }> = ({ message }) => (
<div>{message}</div>
);
// or
const App: React.FC<AppProps> = ({ message }) => <div>{message}</div>;
```
> Tip: You might use [Paul Shen's VS Code Extension](https://marketplace.visualstudio.com/items?itemName=paulshen.paul-typescript-toolkit) to automate the type destructure declaration (incl a [keyboard shortcut](https://twitter.com/_paulshen/status/1392915279466745857?s=20)).
<details>
<summary><b>Why is <code>React.FC</code> not needed? What about <code>React.FunctionComponent</code>/<code>React.VoidFunctionComponent</code>?</b></summary>
You may see this in many React+TypeScript codebases:
```tsx
const App: React.FunctionComponent<{ message: string }> = ({ message }) => (
<div>{message}</div>
);
```
However, the general consensus today is that `React.FunctionComponent` (or the shorthand `React.FC`) is not needed. If you're still using React 17 or TypeScript lower than 5.1, it is even [discouraged](https://github.com/facebook/create-react-app/pull/8177). This is a nuanced opinion of course, but if you agree and want to remove `React.FC` from your codebase, you can use [this jscodeshift codemod](https://github.com/gndelia/codemod-replace-react-fc-typescript).
Some differences from the "normal function" version:
- `React.FunctionComponent` is explicit about the return type, while the normal function version is implicit (or else needs additional annotation).
- It provides typechecking and autocomplete for static properties like `displayName`, `propTypes`, and `defaultProps`.
- Note that there are some known issues using `defaultProps` with `React.FunctionComponent`. See [this issue for details](https://github.com/typescript-cheatsheets/react/issues/87). We maintain a separate `defaultProps` section you can also look up.
- Before the [React 18 type updates](https://github.com/DefinitelyTyped/DefinitelyTyped/pull/56210), `React.FunctionComponent` provided an implicit definition of `children` (see below), which was heavily debated and is one of the reasons [`React.FC` was removed from the Create React App TypeScript template](https://github.com/facebook/create-react-app/pull/8177).
```tsx
// before React 18 types
const Title: React.FunctionComponent<{ title: string }> = ({
children,
title,
}) => <div title={title}>{children}</div>;
```
<details>
<summary>(Deprecated)<b>Using <code>React.VoidFunctionComponent</code> or <code>React.VFC</code> instead</b></summary>
In [@types/react 16.9.48](https://github.com/DefinitelyTyped/DefinitelyTyped/pull/46643), the `React.VoidFunctionComponent` or `React.VFC` type was added for typing `children` explicitly.
However, please be aware that `React.VFC` and `React.VoidFunctionComponent` were deprecated in React 18 (https://github.com/DefinitelyTyped/DefinitelyTyped/pull/59882), so this interim solution is no longer necessary or recommended in React 18+.
Please use regular function components or `React.FC` instead.
```ts
type Props = { foo: string };
// OK now, in future, error
const FunctionComponent: React.FunctionComponent<Props> = ({
foo,
children,
}: Props) => {
return (
<div>
{foo} {children}
</div>
); // OK
};
// Error now, in future, deprecated
const VoidFunctionComponent: React.VoidFunctionComponent<Props> = ({
foo,
children,
}) => {
return (
<div>
{foo}
{children}
</div>
);
};
```
</details>
- _In the future_, it may automatically mark props as `readonly`, though that's a moot point if the props object is destructured in the parameter list.
In most cases it makes very little difference which syntax is used, but you may prefer the more explicit nature of `React.FunctionComponent`.
</details>
<!--END-SECTION:function-components-->
<!--START-SECTION:hooks-->
#### Hooks
Hooks are [supported in `@types/react` from v16.8 up](https://github.com/DefinitelyTyped/DefinitelyTyped/blob/a05cc538a42243c632f054e42eab483ebf1560ab/types/react/index.d.ts#L800-L1031).
#### useState
Type inference works very well for simple values:
```tsx
const [state, setState] = useState(false);
// `state` is inferred to be a boolean
// `setState` only takes booleans
```
See also the [Using Inferred Types](https://react-typescript-cheatsheet.netlify.app/docs/basic/troubleshooting/types/#using-inferred-types) section if you need to use a complex type that you've relied on inference for.
However, many hooks are initialized with null-ish default values, and you may wonder how to provide types. Explicitly declare the type, and use a union type:
```tsx
const [user, setUser] = useState<User | null>(null);
// later...
setUser(newUser);
```
You can also use type assertions if a state is initialized soon after setup and always has a value after:
```tsx
const [user, setUser] = useState<User>({} as User);
// later...
setUser(newUser);
```
This temporarily "lies" to the TypeScript compiler that `{}` is of type `User`. You should follow up by setting the `user` state — if you don't, the rest of your code may rely on the fact that `user` is of type `User` and that may lead to runtime errors.
#### useCallback
You can type the `useCallback` just like any other function.
```ts
const memoizedCallback = useCallback(
(param1: string, param2: number) => {
console.log(param1, param2)
return { ok: true }
},
[...],
);
/**
* VSCode will show the following type:
* const memoizedCallback:
* (param1: string, param2: number) => { ok: boolean }
*/
```
Note that for React < 18, the function signature of `useCallback` typed arguments as `any[]` by default:
```ts
function useCallback<T extends (...args: any[]) => any>(
callback: T,
deps: DependencyList
): T;
```
In React >= 18, the function signature of `useCallback` changed to the following:
```ts
function useCallback<T extends Function>(callback: T, deps: DependencyList): T;
```
Therefore, the following code will yield "`Parameter 'e' implicitly has an 'any' type.`" error in React >= 18, but not <17.
```ts
// @ts-expect-error Parameter 'e' implicitly has 'any' type.
useCallback((e) => {}, []);
// Explicit 'any' type.
useCallback((e: any) => {}, []);
```
#### useReducer
You can use [Discriminated Unions](https://www.typescriptlang.org/docs/handbook/typescript-in-5-minutes-func.html#discriminated-unions) for reducer actions. Don't forget to define the return type of reducer, otherwise TypeScript will infer it.
```tsx
import { useReducer } from "react";
const initialState = { count: 0 };
type ACTIONTYPE =
| { type: "increment"; payload: number }
| { type: "decrement"; payload: string };
function reducer(state: typeof initialState, action: ACTIONTYPE) {
switch (action.type) {
case "increment":
return { count: state.count + action.payload };
case "decrement":
return { count: state.count - Number(action.payload) };
default:
throw new Error();
}
}
function Counter() {
const [state, dispatch] = useReducer(reducer, initialState);
return (
<>
Count: {state.count}
<button onClick={() => dispatch({ type: "decrement", payload: "5" })}>
-
</button>
<button onClick={() => dispatch({ type: "increment", payload: 5 })}>
+
</button>
</>
);
}
```
[View in the TypeScript Playground](https://www.typescriptlang.org/play?#code/LAKFEsFsAcHsCcAuACAVMghgZ2QJQKYYDGKAZvLJMgOTyEnUDcooRsAdliuO+IuBgA2AZUQZE+ZAF5kAbzYBXdogBcyAAwBfZmBCIAntEkBBAMIAVAJIB5AHLmAmgAUAotOShkyAD5zkBozVqHiI6SHxlagAaZGgMfUFYDAATNXYFSAAjfHhNDxAvX1l-Q3wg5PxQ-HDImLiEpNTkLngeAHM8ll1SJRJwDmQ6ZIUiHIAKLnEykqNYUmQePgERMQkY4n4ONTMrO0dXAEo5T2aAdz4iAAtkMY3+9gA6APwj2ROvImxJYPYqmsRqCp3l5BvhEAp4Ow5IplGpJhIHjCUABqTB9DgPeqJFLaYGfLDfCp-CIAoEFEFeOjgyHQ2BKVTNVb4RF05TIAC0yFsGWy8Fu6MeWMaB1x5K8FVIGAUglUwK8iEuFFOyHY+GVLngFD5Bx0Xk0oH13V6myhplZEm1x3JbE4KAA2vD8DFkuAsHFEFcALruAgbB4KAkEYajPlDEY5GKLfhCURTHUnKkQqFjYEAHgAfHLkGb6WpZI6WfTDRSvKnMgpEIgBhxTIJwEQANZSWRjI5SdPIF1u8RXMayZ7lSphEnRWLxbFNagAVmomhF6fZqYA9OXKxxM2KQWWK1WoTW643m63pB2u+7e-3SkEQsPamOGik1FO55p08jl6vdxuKcvv8h4yAmhAA)
<details>
<summary><b>Usage with <code>Reducer</code> from <code>redux</code></b></summary>
In case you use the [redux](https://github.com/reduxjs/redux) library to write reducer function, It provides a convenient helper of the format `Reducer<State, Action>` which takes care of the return type for you.
So the above reducer example becomes:
```tsx
import { Reducer } from 'redux';
export function reducer: Reducer<AppState, Action>() {}
```
</details>
#### useEffect / useLayoutEffect
Both of `useEffect` and `useLayoutEffect` are used for performing <b>side effects</b> and return an optional cleanup function which means if they don't deal with returning values, no types are necessary. When using `useEffect`, take care not to return anything other than a function or `undefined`, otherwise both TypeScript and React will yell at you. This can be subtle when using arrow functions:
```ts
function DelayedEffect(props: { timerMs: number }) {
const { timerMs } = props;
useEffect(
() =>
setTimeout(() => {
/* do stuff */
}, timerMs),
[timerMs]
);
// bad example! setTimeout implicitly returns a number
// because the arrow function body isn't wrapped in curly braces
return null;
}
```
<details>
<summary><b>Solution to the above example</b></summary>
```tsx
function DelayedEffect(props: { timerMs: number }) {
const { timerMs } = props;
useEffect(() => {
setTimeout(() => {
/* do stuff */
}, timerMs);
}, [timerMs]);
// better; use the void keyword to make sure you return undefined
return null;
}
```
</details>
#### useRef
In TypeScript, `useRef` returns a reference that is either [read-only](https://github.com/DefinitelyTyped/DefinitelyTyped/blob/abd69803c1b710db58d511f4544ec1b70bc9077c/types/react/v16/index.d.ts#L1025-L1039) or [mutable](https://github.com/DefinitelyTyped/DefinitelyTyped/blob/abd69803c1b710db58d511f4544ec1b70bc9077c/types/react/v16/index.d.ts#L1012-L1023), depends on whether your type argument fully covers the initial value or not. Choose one that suits your use case.
##### Option 1: DOM element ref
**[To access a DOM element](https://reactjs.org/docs/refs-and-the-dom.html):** provide only the element type as argument, and use `null` as initial value. In this case, the returned reference will have a read-only `.current` that is managed by React. TypeScript expects you to give this ref to an element's `ref` prop:
```tsx
function Foo() {
// - If possible, prefer as specific as possible. For example, HTMLDivElement
// is better than HTMLElement and way better than Element.
// - Technical-wise, this returns RefObject<HTMLDivElement>
const divRef = useRef<HTMLDivElement>(null);
useEffect(() => {
// Note that ref.current may be null. This is expected, because you may
// conditionally render the ref-ed element, or you may forget to assign it
if (!divRef.current) throw Error("divRef is not assigned");
// Now divRef.current is sure to be HTMLDivElement
doSomethingWith(divRef.current);
});
// Give the ref to an element so React can manage it for you
return <div ref={divRef}>etc</div>;
}
```
If you are sure that `divRef.current` will never be null, it is also possible to use the non-null assertion operator `!`:
```tsx
const divRef = useRef<HTMLDivElement>(null!);
// Later... No need to check if it is null
doSomethingWith(divRef.current);
```
Note that you are opting out of type safety here - you will have a runtime error if you forget to assign the ref to an element in the render, or if the ref-ed element is conditionally rendered.
<details>
<summary><b>Tip: Choosing which <code>HTMLElement</code> to use</b></summary>
Refs demand specificity - it is not enough to just specify any old `HTMLElement`. If you don't know the name of the element type you need, you can check [lib.dom.ts](https://github.com/microsoft/TypeScript/blob/v3.9.5/lib/lib.dom.d.ts#L19224-L19343) or make an intentional type error and let the language service tell you:
</details>
##### Option 2: Mutable value ref
**[To have a mutable value](https://reactjs.org/docs/hooks-faq.html#is-there-something-like-instance-variables):** provide the type you want, and make sure the initial value fully belongs to that type:
```tsx
function Foo() {
// Technical-wise, this returns MutableRefObject<number | null>
const intervalRef = useRef<number | null>(null);
// You manage the ref yourself (that's why it's called MutableRefObject!)
useEffect(() => {
intervalRef.current = setInterval(...);
return () => clearInterval(intervalRef.current);
}, []);
// The ref is not passed to any element's "ref" prop
return <button onClick={/* clearInterval the ref */}>Cancel timer</button>;
}
```
##### See also
- [Related issue by @rajivpunjabi](https://github.com/typescript-cheatsheets/react/issues/388) - [Playground](https://www.typescriptlang.org/play#code/JYWwDg9gTgLgBAKjgQwM5wEoFNkGN4BmUEIcARFDvmQNwCwAUI7hAHarwCCYYcAvHAAUASn4A+OAG9GjOHAD0CBLLnKGcxHABiwKBzgQwMYGxS4WUACbBWAczgwIcSxFwBXEFlYxkxtgDoVTQBJVmBjZAAbOAA3KLcsOAB3YEjogCNE1jc0-zgAGQBPG3tHOAAVQrAsAGVcKGAjOHTCuDdUErhWNgBabLSUVFQsWBNWA2qoX2hA9VU4AGFKXyx0AFk3H3TIxOwCOAB5dIArLHwgpHcoSm84MGJJmFbgdG74ZcsDVkjC2Y01f7yFQsdjvLAEACM-EwVBg-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-bfK05SrDA8mWVagHAbZeScOY0CjqUE6uOgqDaRAOSfKqOYgb8KiMaZ9GSeCEIMkyMVyUwRHWYc7nSvAgUQEk6AjMQXpReWyWGdFLHeBZHEuTCQEZT8xVwaV8BxZCzUWZQMDvuMghBHASJVnCWhTLYApiH1chIqgxpGeCfCSIxAC+Yj3o+8YvvgSLyNNOLjeBGhTTNdLzVJy3reGMBbTtrB7RoB3XbNBAneCsHLatcbPhdV3GrdB1WYhw3IKNZq-W2DCLYRO7QPAljgsgORcDwVJAA)
- [Example from Stefan Baumgartner](https://fettblog.eu/typescript-react/hooks/#useref) - [Playground](https://www.typescriptlang.org/play/?jsx=2#code/JYWwDg9gTgLgBAJQKYEMDG8BmUIjgIilQ3wFgAoCzAVwDsNgJa4AVJADxgElaxqYA6sBgALAGIQ01AM4AhfjCYAKAJRwA3hThwA9DrjBaw4CgA2waUjgB3YSLi1qp0wBo4AI35wYSZ6wCeYEgAymhQwGDw1lYoRHCmEBAA1oYA5nCY0HAozAASLACyADI8fDAAoqZIIEi0MFpwaEzS8IZllXAAvIjEMAB0MkjImAA8+cWl-JXVtTAAfEqOzioA3A1NtC1wTPIwirQAwuZoSV1wql1zGg3aenAt4RgOTqaNIkgn0g5ISAAmcDJvBA3h9TsBMAZeFNXjl-lIoEQ6nAOBZ+jddPpPPAmGgrPDEfAUS1pG5hAYvhAITBAlZxiUoRUqjU6m5RIDhOi7iIUF9RFYaqIIP9MlJpABCOCAUHJ0eDzm1oXAAGSKyHtUx9fGzNSacjaPWq6Ea6gI2Z9EUyVRrXV6gC+DRtVu0RBgxuYSnRIzm6O06h0ACpIdlfr9jExSQyOkxTP5GjkPFZBv9bKIDYSmbNpH04ABNFD+CV+nR2636kby+BETCddTlyo27w0zr4HycfC6L0lvUjLH7baHY5Jas7BRMI7AE42uYSUXed6pkY6HtMDulnQruCrCg2oA)
#### useImperativeHandle
Based on this [Stackoverflow answer](https://stackoverflow.com/a/69292925/5415299):
```tsx
// Countdown.tsx
// Define the handle types which will be passed to the forwardRef
export type CountdownHandle = {
start: () => void;
};
type CountdownProps = {};
const Countdown = forwardRef<CountdownHandle, CountdownProps>((props, ref) => {
useImperativeHandle(ref, () => ({
// start() has type inference here
start() {
alert("Start");
},
}));
return <div>Countdown</div>;
});
```
```tsx
// The component uses the Countdown component
import Countdown, { CountdownHandle } from "./Countdown.tsx";
function App() {
const countdownEl = useRef<CountdownHandle>(null);
useEffect(() => {
if (countdownEl.current) {
// start() has type inference here as well
countdownEl.current.start();
}
}, []);
return <Countdown ref={countdownEl} />;
}
```
##### See also:
- [Using ForwardRefRenderFunction](https://stackoverflow.com/a/62258685/5415299)
#### Custom Hooks
If you are returning an array in your Custom Hook, you will want to avoid type inference as TypeScript will infer a union type (when you actually want different types in each position of the array). Instead, use [TS 3.4 const assertions](https://devblogs.microsoft.com/typescript/announcing-typescript-3-4/#const-assertions):
```tsx
import { useState } from "react";
export function useLoading() {
const [isLoading, setState] = useState(false);
const load = (aPromise: Promise<any>) => {
setState(true);
return aPromise.finally(() => setState(false));
};
return [isLoading, load] as const; // infers [boolean, typeof load] instead of (boolean | typeof load)[]
}
```
[View in the TypeScript Playground](https://www.typescriptlang.org/play/?target=5&jsx=2#code/JYWwDg9gTgLgBAJQKYEMDG8BmUIjgcilQ3wFgAoCpAD0ljkwFcA7DYCZuRgZyQBkIKACbBmAcwAUASjgBvCnDhoO3eAG1g3AcNFiANHF4wAyjBQwkAXTgBeRMRgA6HklPmkEzCgA2vKQG4FJRV4b0EhWzgJFAAFHBBNJAAuODjcRIAeFGYATwA+GRs8uSDFIzcLCRgoRiQA0rgiGEYoTlj4xMdMUR9vHIlpW2Lys0qvXzr68kUAX0DpxqRm1rgNLXDdAzDhaxRuYOZVfzgAehO4UUwkKH21ACMICG9UZgMYHLAkCEw4baFrUSqVARb5RB5PF5wAA+cHen1BfykaksFBmQA)
This way, when you destructure you actually get the right types based on destructure position.
<details>
<summary><b>Alternative: Asserting a tuple return type</b></summary>
If you are [having trouble with const assertions](https://github.com/babel/babel/issues/9800), you can also assert or define the function return types:
```tsx
import { useState } from "react";
export function useLoading() {
const [isLoading, setState] = useState(false);
const load = (aPromise: Promise<any>) => {
setState(true);
return aPromise.finally(() => setState(false));
};
return [isLoading, load] as [
boolean,
(aPromise: Promise<any>) => Promise<any>
];
}
```
A helper function that automatically types tuples can also be helpful if you write a lot of custom hooks:
```tsx
function tuplify<T extends any[]>(...elements: T) {
return elements;
}
function useArray() {
const numberValue = useRef(3).current;
const functionValue = useRef(() => {}).current;
return [numberValue, functionValue]; // type is (number | (() => void))[]
}
function useTuple() {
const numberValue = useRef(3).current;
const functionValue = useRef(() => {}).current;
return tuplify(numberValue, functionValue); // type is [number, () => void]
}
```
</details>
Note that the React team recommends that custom hooks that return more than two values should use proper objects instead of tuples, however.
#### More Hooks + TypeScript reading:
- https://medium.com/@jrwebdev/react-hooks-in-typescript-88fce7001d0d
- https://fettblog.eu/typescript-react/hooks/#useref
If you are writing a React Hooks library, don't forget that you should also expose your types for users to use.
#### Example React Hooks + TypeScript Libraries:
- https://github.com/mweststrate/use-st8
- https://github.com/palmerhq/the-platform
- https://github.com/sw-yx/hooks
[Something to add? File an issue](https://github.com/typescript-cheatsheets/react/issues/new).
<!--END-SECTION:hooks-->
<!--START-SECTION:class-components-->
#### Class Components
Within TypeScript, `React.Component` is a generic type (aka `React.Component<PropType, StateType>`), so you want to provide it with (optional) prop and state type parameters:
```tsx
type MyProps = {
// using `interface` is also ok
message: string;
};
type MyState = {
count: number; // like this
};
class App extends React.Component<MyProps, MyState> {
state: MyState = {
// optional second annotation for better type inference
count: 0,
};
render() {
return (
<div>
{this.props.message} {this.state.count}
</div>
);
}
}
```
[View in the TypeScript Playground](https://www.typescriptlang.org/play/?jsx=2#code/JYWwDg9gTgLgBAJQKYEMDG8BmUIjgcilQ3wFgAoCmATzCTgFlqAFHMAZzgF44BvCuHAD0QuAFd2wAHYBzOAANpMJFEzok8uME4oANuwhwIAawFwQSduxQykALjjsYUaTIDcFAL4fyNOo2oAZRgUZW4+MzQIMSkYBykxEAAjFTdhUV1gY3oYAAttLx80XRQrOABBMDA4JAAPZSkAE05kdBgAOgBhXEgpJFiAHiZWCA4AGgDg0KQAPgjyQSdphyYpsJ5+BcF0ozAYYAgpPUckKKa4FCkpCBD9w7hMaDgUmGUoOD96aUwVfrQkMyCKIxOJwAAMZm8ZiITRUAAoAJTzbZwIgwMRQKRwOGA7YDRrAABuM1xKN4eW07TAbHY7QsVhsSE8fAptKWynawNinlJcAGQgJxNxCJ8gh55E8QA)
Don't forget that you can export/import/extend these types/interfaces for reuse.
<details>
<summary><b>Why annotate <code>state</code> twice?</b></summary>
It isn't strictly necessary to annotate the `state` class property, but it allows better type inference when accessing `this.state` and also initializing the state.
This is because they work in two different ways, the 2nd generic type parameter will allow `this.setState()` to work correctly, because that method comes from the base class, but initializing `state` inside the component overrides the base implementation so you have to make sure that you tell the compiler that you're not actually doing anything different.
[See commentary by @ferdaber here](https://github.com/typescript-cheatsheets/react/issues/57).
</details>
<details>
<summary><b>No need for <code>readonly</code></b></summary>
You often see sample code include `readonly` to mark props and state immutable:
```tsx
type MyProps = {
readonly message: string;
};
type MyState = {
readonly count: number;
};
```
This is not necessary as `React.Component<P,S>` already marks them as immutable. ([See PR and discussion!](https://github.com/DefinitelyTyped/DefinitelyTyped/pull/26813))
</details>
**Class Methods**: Do it like normal, but just remember any arguments for your functions also need to be typed:
```tsx
class App extends React.Component<{ message: string }, { count: number }> {
state = { count: 0 };
render() {
return (
<div onClick={() => this.increment(1)}>
{this.props.message} {this.state.count}
</div>
);
}
increment = (amt: number) => {
// like this
this.setState((state) => ({
count: state.count + amt,
}));
};
}
```
[View in the TypeScript Playground](https://www.typescriptlang.org/play/?jsx=2#code/JYWwDg9gTgLgBAJQKYEMDG8BmUIjgcilQ3wFgAoCtAGxQGc64BBMMOJADxiQDsATRsnQwAdAGFckHrxgAeAN5wQSBigDmSAFxw6MKMB5q4AXwA0cRWggBXHjG09rIAEZIoJgHwWKcHTBTccAC8FnBWtvZwAAwmANw+cET8bgAUAJTe5L6+RDDWUDxwKQnZcLJ8wABucBA8YtTAaADWQfLpwV4wABbAdCIGaETKdikAjGnGHiWlFt29ImA4YH3KqhrGsz19ugFIIuF2xtO+sgD0FZVTWdlp8ddH1wNDMsFFKCCRji5uGUFe8tNTqc4A0mkg4HM6NNISI6EgYABlfzcFI7QJ-IoA66lA6RNF7XFwADUcHeMGmxjStwSxjuxiAA)
**Class Properties**: If you need to declare class properties for later use, just declare it like `state`, but without assignment:
```tsx
class App extends React.Component<{
message: string;
}> {
pointer: number; // like this
componentDidMount() {
this.pointer = 3;
}
render() {
return (
<div>
{this.props.message} and {this.pointer}
</div>
);
}
}
```
[View in the TypeScript Playground](https://www.typescriptlang.org/play/?jsx=2#code/JYWwDg9gTgLgBAJQKYEMDG8BmUIjgcilQ3wFgAoCtAGxQGc64BBMMOJADxiQDsATRsnQwAdAGFckHrxgAeAN4U4cEEgYoA5kgBccOjCjAeGgNwUAvgD44i8sshHuUXTwCuIAEZIoJuAHo-OGpgAGskOBgAC2A6JTg0SQhpHhgAEWA+AFkIVxSACgBKGzjlKJiRBxTvOABeOABmMzs4cziifm9C4ublIhhXKB44PJLlOFk+YAA3S1GxmzK6CpwwJdV1LXM4FH4F6KXKp1aesdk-SZnRgqblY-MgA)
[Something to add? File an issue](https://github.com/typescript-cheatsheets/react/issues/new).
#### Typing getDerivedStateFromProps
Before you start using `getDerivedStateFromProps`, please go through the [documentation](https://reactjs.org/docs/react-component.html#static-getderivedstatefromprops) and [You Probably Don't Need Derived State](https://reactjs.org/blog/2018/06/07/you-probably-dont-need-derived-state.html). Derived State can be implemented using hooks which can also help set up memoization.
Here are a few ways in which you can annotate `getDerivedStateFromProps`
1. If you have explicitly typed your derived state and want to make sure that the return value from `getDerivedStateFromProps` conforms to it.
```tsx
class Comp extends React.Component<Props, State> {
static getDerivedStateFromProps(
props: Props,
state: State
): Partial<State> | null {
//
}
}
```
2. When you want the function's return value to determine your state.
```tsx
class Comp extends React.Component<
Props,
ReturnType<typeof Comp["getDerivedStateFromProps"]>
> {
static getDerivedStateFromProps(props: Props) {}
}
```
3. When you want derived state with other state fields and memoization
```tsx
type CustomValue = any;
interface Props {
propA: CustomValue;
}
interface DefinedState {
otherStateField: string;
}
type State = DefinedState & ReturnType<typeof transformPropsToState>;
function transformPropsToState(props: Props) {
return {
savedPropA: props.propA, // save for memoization
derivedState: props.propA,
};
}
class Comp extends React.PureComponent<Props, State> {
constructor(props: Props) {
super(props);
this.state = {
otherStateField: "123",
...transformPropsToState(props),
};
}
static getDerivedStateFromProps(props: Props, state: State) {
if (isEqual(props.propA, state.savedPropA)) return null;
return transformPropsToState(props);
}
}
```
[View in the TypeScript Playground](https://www.typescriptlang.org/play/?jsx=2#code/JYWwDg9gTgLgBAJQKYEMDG8BmUIjgcilQ3wFgAoUSWOYAZwFEBHAVxQBs5tcD2IATFHQAWAOnpJWHMuQowAnmCRwAwizoxcANQ4tlAXjgoAdvIDcFYMZhIomdMoAKOMHTgBvCnDhgXAQQAuVXVNEB12PQtyAF9La1t7NGUAESRMKyR+AGUYFBsPLzgIGGFbHLykADFgJHZ+II0oKwBzKNjyBSU4cvzDVPTjTJ7lADJEJBgWKGMAFUUkAB5OpAhMOBgoEzpMaBBnCFcZiGGAPijMFmMMYAhjdc3jbd39w+PcmwAKXwO6IJe6ACUBXI3iIk2mwO83joKAAbpkXoEfC46KJvmA-AAaOAAehxcBh8K40DgICQIAgwAAXnkbsZCt5+LZgPDsu8kEF0aj0X5CtE2hQ0OwhG4VLgwHAkAAPGzGfhuZDoGCiRxTJBi8C3JDWBb-bGnSFwNC3RosDDQL4ov4ooGeEFQugsJRQS0-AFRKHrYT0UQaCpwQx2z3eYqlKDDaq1epwABEAEYAEwAZhjmIZUNEmY2Wx2UD2KKOw1drgB6f5fMKfpgwDQcGaE1STVZEZw+Z+xd+cD1BPZQWGtvTwDWH3ozDY7A7aP82KrSF9cIR-gBQLBUzuxhY7HYHqhq4h2ceubbryLXPdFZiQA)
<!--END-SECTION:class-components-->
<!--START-SECTION:default-props-->
#### You May Not Need `defaultProps`
As per [this tweet](https://twitter.com/dan_abramov/status/1133878326358171650), defaultProps will eventually be deprecated. You can check the discussions here:
- [Original tweet](https://twitter.com/hswolff/status/1133759319571345408)
- More info can also be found in [this article](https://medium.com/@matanbobi/react-defaultprops-is-dying-whos-the-contender-443c19d9e7f1)
The consensus is to use object default values.
Function Components:
```tsx
type GreetProps = { age?: number };
const Greet = ({ age = 21 }: GreetProps) => // etc
```
Class Components:
```tsx
type GreetProps = {
age?: number;
};
class Greet extends React.Component<GreetProps> {
render() {
const { age = 21 } = this.props;
/*...*/
}
}
let el = <Greet age={3} />;
```
#### Typing `defaultProps`
Type inference improved greatly for `defaultProps` in [TypeScript 3.0+](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-0.html), although [some edge cases are still problematic](https://github.com/typescript-cheatsheets/react/issues/61).
**Function Components**
```tsx
// using typeof as a shortcut; note that it hoists!
// you can also declare the type of DefaultProps if you choose
// e.g. https://github.com/typescript-cheatsheets/react/issues/415#issuecomment-841223219
type GreetProps = { age: number } & typeof defaultProps;
const defaultProps = {
age: 21,
};
const Greet = (props: GreetProps) => {
// etc
};
Greet.defaultProps = defaultProps;
```
_[See this in TS Playground](https://www.typescriptlang.org/play?#code/JYWwDg9gTgLgBAKjgQwM5wEoFNkGN4BmUEIcARFDvmQNwBQdMAnmFnAOKVYwAKxY6ALxwA3igDmWAFxwAdgFcQAIyxQ4AXzgAyOM1YQCcACZYCyeQBte-VPVwRZqeCbOXrEAXGEi6cCdLgAJgBGABo6dXo6e0d4TixuLzgACjAbGXjuPg9UAEovAD5RXzhKGHkoWTgAHiNgADcCkTScgDpkSTgAeiQFZVVELvVqrrrGiPpMmFaXcytsz2FZtwXbOiA)_
For **Class components**, there are [a couple ways to do it](https://github.com/typescript-cheatsheets/react/pull/103#issuecomment-481061483) (including using the `Pick` utility type) but the recommendation is to "reverse" the props definition:
```tsx
type GreetProps = typeof Greet.defaultProps & {
age: number;
};
class Greet extends React.Component<GreetProps> {
static defaultProps = {
age: 21,
};
/*...*/
}
// Type-checks! No type assertions needed!
let el = <Greet age={3} />;
```
<details>
<summary><b><code>React.JSX.LibraryManagedAttributes</code> nuance for library authors</b></summary>
The above implementations work fine for App creators, but sometimes you want to be able to export `GreetProps` so that others can consume it. The problem here is that the way `GreetProps` is defined, `age` is a required prop when it isn't because of `defaultProps`.
The insight to have here is that [`GreetProps` is the _internal_ contract for your component, not the _external_, consumer facing contract](https://github.com/typescript-cheatsheets/react/issues/66#issuecomment-453878710). You could create a separate type specifically for export, or you could make use of the `React.JSX.LibraryManagedAttributes` utility:
```tsx
// internal contract, should not be exported out
type GreetProps = {
age: number;
};
class Greet extends Component<GreetProps> {
static defaultProps = { age: 21 };
}
// external contract
export type ApparentGreetProps = React.JSX.LibraryManagedAttributes<
typeof Greet,
GreetProps
>;
```
This will work properly, although hovering over`ApparentGreetProps`may be a little intimidating. You can reduce this boilerplate with the`ComponentProps` utility detailed below.
</details>
#### Consuming Props of a Component with defaultProps
A component with `defaultProps` may seem to have some required props that actually aren't.
##### Problem Statement
Here's what you want to do:
```tsx
interface IProps {
name: string;
}
const defaultProps = {
age: 25,
};
const GreetComponent = ({ name, age }: IProps & typeof defaultProps) => (
<div>{`Hello, my name is ${name}, ${age}`}</div>
);
GreetComponent.defaultProps = defaultProps;
const TestComponent = (props: React.ComponentProps<typeof GreetComponent>) => {
return <h1 />;
};
// Property 'age' is missing in type '{ name: string; }' but required in type '{ age: number; }'
const el = <TestComponent name="foo" />;
```
##### Solution
Define a utility that applies `React.JSX.LibraryManagedAttributes`:
```tsx
type ComponentProps<T> = T extends
| React.ComponentType<infer P>
| React.Component<infer P>
? React.JSX.LibraryManagedAttributes<T, P>
: never;
const TestComponent = (props: ComponentProps<typeof GreetComponent>) => {
return <h1 />;
};
// No error
const el = <TestComponent name="foo" />;
```
[_See this in TS Playground_](https://www.typescriptlang.org/play?#code/JYWwDg9gTgLgBAKjgQwM5wEoFNkGN4BmUEIcARFDvmQNwBQdMAnmFnAMImQB2W3MABWJhUAHgAqAPjgBeOOLhYAHjD4ATdNjwwAdJ3ARe-cSyyjg3AlihwB0gD6Yqu-Tz4xzl67cl04cAH44ACkAZQANHQAZYAAjKGQoJgBZZG5kAHMsNQBBGBgoOIBXVTFxABofPzgALjheADdrejoLVSgCPDYASSEIETgAb2r0kCw61AKLDPoAXzpcQ0m4NSxOooAbQWF0OWH-TPG4ACYAVnK6WfpF7mWAcUosGFdDd1k4AApB+uQxysO4LM6r0dnAAGRwZisCAEFZrZCbbb9VAASlk0g+1VEamADUkgwABgAJLAbDYQSogJg-MZwYDoAAkg1GWFmlSZh1mBNmogA9Di8XQUfQHlgni8jLpVustn0BnJpQjZTsWrzeXANsh2gwbstxFhJhK3nIPmAdnUjfw5WIoVgYXBReKuK9+JI0TJpPs4JQYEUoNw4KIABYARjgvN8VwYargADkIIooMQoAslvBSe8JAbns7JTSsDIyAQIBAyOHJDQgA)