React & Redux in TypeScript - Complete Guide & tutorial

"This guide is a living compendium documenting the most important patterns and recipes on how to use React (and its Ecosystem) in a functional style using TypeScript. It will help you make your code completely type-safe while focusing on inferring the types from implementation so there is less noise coming from excessive type annotations and it's easier to write and maintain correct types in the long run."

Goals

• Complete type safety (with --strict flag) without losing type information downstream through all the layers of our application (e.g. no type assertions or hacking with any type)
• Make type annotations concise by eliminating redundancy in types using advanced TypeScript Language features like Type Inference and Control flow analysis
• Reduce repetition and complexity of types with TypeScript focused complementary libraries

React, Redux, Typescript Ecosystem

• typesafe-actions - Typesafe utilities for "action-creators" in Redux / Flux Architecture
• utility-types - Collection of generic types for TypeScript, complementing built-in mapped types and aliases - think lodash for reusable types.
• react-redux-typescript-scripts - dev-tools configuration files shared between projects based on this guide

Examples

• Todo-App playground: Codesandbox
• React, Redux, TypeScript - RealWorld App: Github | Demo

Installation

Type-Definitions for React & Redux

npm i -D @types/react @types/react-dom @types/react-redux

"react" - @types/react
"react-dom" - @types/react-dom
"redux" - (types included with npm package)*
"react-redux" - @types/react-redux

*NB: Guide is based on types for Redux >= v4.x.x. To make it work with Redux v3.x.x please refer to this config)

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---

React - Type-Definitions Cheatsheet

React.FC<Props> | React.FunctionComponent<Props>

Type representing a functional component

const MyComponent: React.FC<Props> = ...

React.Component<Props, State>

Type representing a class component

class MyComponent extends React.Component<Props, State> { ...

React.ComponentType<Props>

Type representing union of (React.FC | React.Component) - used in HOC

const withState = <P extends WrappedComponentProps>(
  WrappedComponent: React.ComponentType<P>,
) => { ...

React.ComponentProps<typeof XXX>

Gets Props type of a specified component XXX (WARNING: does not work with statically declared default props and generic props)

type MyComponentProps = React.ComponentProps<typeof MyComponent>;

React.ReactElement | JSX.Element

Type representing a concept of React Element - representation of a native DOM component (e.g. <div />), or a user-defined composite component (e.g. <MyComponent />)

const elementOnly: React.ReactElement = <div /> || <MyComponent />;

React.ReactNode

Type representing any possible type of React node (basically ReactElement (including Fragments and Portals) + primitive JS types)

const elementOrPrimitive: React.ReactNode = 'string' || 0 || false || null || undefined || <div /> || <MyComponent />;
const Component = ({ children: React.ReactNode }) => ...

React.CSSProperties

Type representing style object in JSX - for css-in-js styles

const styles: React.CSSProperties = { flexDirection: 'row', ...
const element = <div style={styles} ...

React.HTMLProps<HTMLXXXElement>

Type representing Props of specified HTML Element - for extending HTML Elements

const Input: React.FC<Props & React.HTMLProps<HTMLInputElement>> = props => { ... }

<Input about={...} accept={...} alt={...} ... />

React.ReactEventHandler<HTMLXXXElement>

Type representing generic event handler - for declaring event handlers

const handleChange: React.ReactEventHandler<HTMLInputElement> = (ev) => { ... } 

<input onChange={handleChange} ... />

React.XXXEvent<HTMLXXXElement>

Type representing more specific event. Some common event examples: ChangeEvent, FormEvent, FocusEvent, KeyboardEvent, MouseEvent, DragEvent, PointerEvent, WheelEvent, TouchEvent.

const handleChange = (ev: React.MouseEvent<HTMLDivElement>) => { ... }

<div onMouseMove={handleChange} ... />

In code above React.MouseEvent<HTMLDivElement> is type of mouse event, and this event happened on HTMLDivElement

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---

React - Typing Patterns

Function Components - FC

- Counter Component

import * as React from 'react';

type Props = {
  label: string;
  count: number;
  onIncrement: () => void;
};

export const FCCounter: React.FC<Props> = props => {
  const { label, count, onIncrement } = props;

  const handleIncrement = () => {
    onIncrement();
  };

  return (
    <div>
      <span>
        {label}: {count}
      </span>
      <button type="button" onClick={handleIncrement}>
        {`Increment`}
      </button>
    </div>
  );
};

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- Spreading attributes in Component

import * as React from 'react';

type Props = {
  className?: string;
  style?: React.CSSProperties;
};

export const FCSpreadAttributes: React.FC<Props> = props => {
  const { children, ...restProps } = props;

  return <div {...restProps}>{children}</div>;
};

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---

Class Components

- Class Counter Component

import * as React from 'react';

type Props = {
  label: string;
};

type State = {
  count: number;
};

export class ClassCounter extends React.Component<Props, State> {
  readonly state: State = {
    count: 0,
  };

  handleIncrement = () => {
    this.setState({ count: this.state.count + 1 });
  };

  render() {
    const { handleIncrement } = this;
    const { label } = this.props;
    const { count } = this.state;

    return (
      <div>
        <span>
          {label}: {count}
        </span>
        <button type="button" onClick={handleIncrement}>
          {`Increment`}
        </button>
      </div>
    );
  }
}

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- Class Component with default props

import * as React from 'react';

type Props = {
  label: string;
  initialCount: number;
};

type State = {
  count: number;
};

export class ClassCounterWithDefaultProps extends React.Component<
  Props,
  State
> {
  static defaultProps = {
    initialCount: 0,
  };

  readonly state: State = {
    count: this.props.initialCount,
  };

  handleIncrement = () => {
    this.setState({ count: this.state.count + 1 });
  };

  render() {
    const { handleIncrement } = this;
    const { label } = this.props;
    const { count } = this.state;

    return (
      <div>
        <span>
          {label}: {count}
        </span>
        <button type="button" onClick={handleIncrement}>
          {`Increment`}
        </button>
      </div>
    );
  }
}

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---

Generic Components

• easily create typed component variations and reuse common logic
• common use case is a generic list components

- Generic List Component

import * as React from 'react';

export interface GenericListProps<T> {
  items: T[];
  itemRenderer: (item: T) => JSX.Element;
}

export class GenericList<T> extends React.Component<GenericListProps<T>, {}> {
  render() {
    const { items, itemRenderer } = this.props;

    return (
      <div>
        {items.map(itemRenderer)}
      </div>
    );
  }
}

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Render Props

https://reactjs.org/docs/render-props.html

- Name Provider Component

simple component using children as a render prop

import * as React from 'react';

interface NameProviderProps {
  children: (state: NameProviderState) => React.ReactNode;
}

interface NameProviderState {
  readonly name: string;
}

export class NameProvider extends React.Component<NameProviderProps, NameProviderState> {
  readonly state: NameProviderState = { name: 'Piotr' };

  render() {
    return this.props.children(this.state);
  }
}

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- Mouse Provider Component

Mouse component found in Render Props React Docs

import * as React from 'react';

export interface MouseProviderProps {
  render: (state: MouseProviderState) => React.ReactNode;
}

interface MouseProviderState {
  readonly x: number;
  readonly y: number;
}

export class MouseProvider extends React.Component<MouseProviderProps, MouseProviderState> {
  readonly state: MouseProviderState = { x: 0, y: 0 };

  handleMouseMove = (event: React.MouseEvent<HTMLDivElement>) => {
    this.setState({
      x: event.clientX,
      y: event.clientY,
    });
  };

  render() {
    return (
      <div style={{ height: '100%' }} onMouseMove={this.handleMouseMove}>
        {/*
          Instead of providing a static representation of what <Mouse> renders,
          use the `render` prop to dynamically determine what to render.
        */}
        {this.props.render(this.state)}
      </div>
    );
  }
}

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---

Higher-Order Components

https://reactjs.org/docs/higher-order-components.html

- HOC wrapping a component

Adds state to a stateless counter

import React from 'react';
import { Diff } from 'utility-types';

// These props will be injected into the base component
interface InjectedProps {
  count: number;
  onIncrement: () => void;
}

export const withState = <BaseProps extends InjectedProps>(
  BaseComponent: React.ComponentType<BaseProps>
) => {
  type HocProps = Diff<BaseProps, InjectedProps> & {
    // here you can extend hoc with new props
    initialCount?: number;
  };
  type HocState = {
    readonly count: number;
  };

  return class Hoc extends React.Component<HocProps, HocState> {
    // Enhance component name for debugging and React-Dev-Tools
    static displayName = `withState(${BaseComponent.name})`;
    // reference to original wrapped component
    static readonly WrappedComponent = BaseComponent;

    readonly state: HocState = {
      count: Number(this.props.initialCount) || 0,
    };

    handleIncrement = () => {
      this.setState({ count: this.state.count + 1 });
    };

    render() {
      const { ...restProps } = this.props;
      const { count } = this.state;

      return (
        <BaseComponent
          count={count} // injected
          onIncrement={this.handleIncrement} // injected
          {...(restProps as BaseProps)}
        />
      );
    }
  };
};

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- HOC wrapping a component and injecting props

Adds error handling using componentDidCatch to any component

import React from 'react';

const MISSING_ERROR = 'Error was swallowed during propagation.';

export const withErrorBoundary = <BaseProps extends {}>(
  BaseComponent: React.ComponentType<BaseProps>
) => {
  type HocProps = {
    // here you can extend hoc with new props
  };
  type HocState = {
    readonly error: Error | null | undefined;
  };

  return class Hoc extends React.Component<HocProps, HocState> {
    // Enhance component name for debugging and React-Dev-Tools
    static displayName = `withErrorBoundary(${BaseComponent.name})`;
    // reference to original wrapped component
    static readonly WrappedComponent = BaseComponent;

    readonly state: HocState = {
      error: undefined,
    };

    componentDidCatch(error: Error | null, info: object) {
      this.setState({ error: error || new Error(MISSING_ERROR) });
      this.logErrorToCloud(error, info);
    }

    logErrorToCloud = (error: Error | null, info: object) => {
      // TODO: send error report to service provider
    };

    render() {
      const { children, ...restProps } = this.props;
      const { error } = this.state;

      if (error) {
        return <BaseComponent {...(restProps as BaseProps)} />;
      }

      return children;
    }
  };
};

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- Nested HOC - wrapping a component, injecting props and connecting to redux 

Adds error handling using componentDidCatch to any component

import { RootState } from 'MyTypes';
import React from 'react';
import { connect } from 'react-redux';
import { Diff } from 'utility-types';
import { countersActions, countersSelectors } from '../features/counters';

// These props will be injected into the base component
interface InjectedProps {
  count: number;
  onIncrement: () => void;
}

export const withConnectedCount = <BaseProps extends InjectedProps>(
  BaseComponent: React.ComponentType<BaseProps>
) => {
  const mapStateToProps = (state: RootState) => ({
    count: countersSelectors.getReduxCounter(state.counters),
  });

  const dispatchProps = {
    onIncrement: countersActions.increment,
  };

  type HocProps = ReturnType<typeof mapStateToProps> &
    typeof dispatchProps & {
      // here you can extend ConnectedHoc with new props
      overrideCount?: number;
    };

  class Hoc extends React.Component<HocProps> {
    // Enhance component name for debugging and React-Dev-Tools
    static displayName = `withConnectedCount(${BaseComponent.name})`;
    // reference to original wrapped component
    static readonly WrappedComponent = BaseComponent;

    render() {
      const { count, onIncrement, overrideCount, ...restProps } = this.props;

      return (
        <BaseComponent
          count={overrideCount || count} // injected
          onIncrement={onIncrement} // injected
          {...(restProps as BaseProps)}
        />
      );
    }
  }

  const ConnectedHoc = connect<
    ReturnType<typeof mapStateToProps>,
    typeof dispatchProps, // use "undefined" if NOT using dispatchProps
    Diff<BaseProps, InjectedProps>,
    RootState
  >(
    mapStateToProps,
    dispatchProps
  )(Hoc);

  return ConnectedHoc;
};

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---

Redux Connected Components

- Redux connected counter

import Types from 'MyTypes';
import { connect } from 'react-redux';

import { countersActions, countersSelectors } from '../features/counters';
import { FCCounter } from '../components';

const mapStateToProps = (state: Types.RootState) => ({
  count: countersSelectors.getReduxCounter(state.counters),
});

const dispatchProps = {
  onIncrement: countersActions.increment,
};

export const FCCounterConnected = connect(
  mapStateToProps,
  dispatchProps
)(FCCounter);

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- Redux connected counter with own props

import Types from 'MyTypes';
import { connect } from 'react-redux';

import { countersActions, countersSelectors } from '../features/counters';
import { FCCounter } from '../components';

type OwnProps = {
  initialCount?: number;
};

const mapStateToProps = (state: Types.RootState, ownProps: OwnProps) => ({
  count:
    countersSelectors.getReduxCounter(state.counters) +
    (ownProps.initialCount || 0),
});

const dispatchProps = {
  onIncrement: countersActions.increment,
};

export const FCCounterConnectedOwnProps = connect(
  mapStateToProps,
  dispatchProps
)(FCCounter);

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- Redux connected counter with redux-thunk integration

import Types from 'MyTypes';
import { bindActionCreators, Dispatch } from 'redux';
import { connect } from 'react-redux';
import * as React from 'react';

import { countersActions } from '../features/counters';

// Thunk Action
const incrementWithDelay = () => async (dispatch: Dispatch): Promise<void> => {
  setTimeout(() => dispatch(countersActions.increment()), 1000);
};

const mapStateToProps = (state: Types.RootState) => ({
  count: state.counters.reduxCounter,
});

const mapDispatchToProps = (dispatch: Dispatch<Types.RootAction>) =>
  bindActionCreators(
    {
      onIncrement: incrementWithDelay,
    },
    dispatch
  );

type Props = ReturnType<typeof mapStateToProps> &
  ReturnType<typeof mapDispatchToProps> & {
    label: string;
  };

export const FCCounter: React.FC<Props> = props => {
  const { label, count, onIncrement } = props;

  const handleIncrement = () => {
    // Thunk action is correctly typed as promise
    onIncrement().then(() => {
      // ...
    });
  };

  return (
    <div>
      <span>
        {label}: {count}
      </span>
      <button type="button" onClick={handleIncrement}>
        {`Increment`}
      </button>
    </div>
  );
};

export const FCCounterConnectedBindActionCreators = connect(
  mapStateToProps,
  mapDispatchToProps
)(FCCounter);

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Context

https://reactjs.org/docs/context.html

ThemeContext

import * as React from 'react';

export type Theme = React.CSSProperties;

type Themes = {
  dark: Theme;
  light: Theme;
};

export const themes: Themes = {
  dark: {
    color: 'black',
    backgroundColor: 'white',
  },
  light: {
    color: 'white',
    backgroundColor: 'black',
  },
};

export type ThemeContextProps = { theme: Theme; toggleTheme?: () => void };
const ThemeContext = React.createContext<ThemeContextProps>({ theme: themes.light });

export default ThemeContext;

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ThemeProvider

import React from 'react';
import ThemeContext, { themes, Theme } from './theme-context';
import ToggleThemeButton from './theme-consumer';

interface State {
  theme: Theme;
}
export class ThemeProvider extends React.Component<{}, State> {
  readonly state: State = { theme: themes.light };

  toggleTheme = () => {
    this.setState(state => ({
      theme: state.theme === themes.light ? themes.dark : themes.light,
    }));
  }

  render() {
    const { theme } = this.state;
    const { toggleTheme } = this;
    return (
      <ThemeContext.Provider value={{ theme, toggleTheme }}>
        <ToggleThemeButton />
      </ThemeContext.Provider>
    );
  }
}

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ThemeConsumer

import * as React from 'react';
import ThemeContext from './theme-context';

type Props = {};

export default function ToggleThemeButton(props: Props) {
  return (
    <ThemeContext.Consumer>
      {({ theme, toggleTheme }) => <button style={theme} onClick={toggleTheme} {...props} />}
    </ThemeContext.Consumer>
  );
}

ThemeConsumer in class component

import * as React from 'react';
import ThemeContext from './theme-context';

type Props = {};

export class ToggleThemeButtonClass extends React.Component<Props> {
  static contextType = ThemeContext;
  context!: React.ContextType<typeof ThemeContext>;

  render() {
    const { theme, toggleTheme } = this.context;
    return (
      <button style={theme} onClick={toggleTheme}>
        Toggle Theme
      </button>
    );
  }
}

Implementation with Hooks

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Hooks

https://reactjs.org/docs/hooks-intro.html

- useState

https://reactjs.org/docs/hooks-reference.html#usestate

import * as React from 'react';

type Props = { initialCount: number };

export default function Counter({initialCount}: Props) {
  const [count, setCount] = React.useState(initialCount);
  return (
    <>
      Count: {count}
      <button onClick={() => setCount(initialCount)}>Reset</button>
      <button onClick={() => setCount(prevCount => prevCount + 1)}>+</button>
      <button onClick={() => setCount(prevCount => prevCount - 1)}>-</button>
    </>
  );
}

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- useReducer

Hook for state management like Redux in a function component.

import * as React from 'react';

interface State {
  count: number;
}

type Action = { type: 'reset' } | { type: 'increment' } | { type: 'decrement' };

function reducer(state: State, action: Action): State {
  switch (action.type) {
    case 'increment':
      return { count: state.count + 1 };
    case 'decrement':
      return { count: state.count - 1 };
    case 'reset':
      return { count: 0 };
    default:
      throw new Error();
  }
}

interface CounterProps {
  initialCount: number;
}

function Counter({ initialCount }: CounterProps) {
  const [state, dispatch] = React.useReducer(reducer, {
    count: initialCount,
  });

  return (
    <>
      Count: {state.count}
      <button onClick={() => dispatch({ type: 'reset' })}>Reset</button>
      <button onClick={() => dispatch({ type: 'increment' })}>+</button>
      <button onClick={() => dispatch({ type: 'decrement' })}>-</button>
    </>
  );
}

export default Counter;

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- useContext

https://reactjs.org/docs/hooks-reference.html#usecontext

import * as React from 'react';
import ThemeContext from '../context/theme-context';

type Props = {};

export default function ThemeToggleButton(props: Props) {
  const { theme, toggleTheme } = React.useContext(ThemeContext);
  return (
    <button onClick={toggleTheme} style={theme} >
      Toggle Theme
    </button>
  );
}

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Redux - Typing Patterns

Store Configuration

Create Global Store Types

RootState - type representing root state-tree

Can be imported in connected components to provide type-safety to Redux connect function

RootAction - type representing union type of all action objects

Can be imported in various layers receiving or sending redux actions like: reducers, sagas or redux-observables epics

import { StateType, ActionType } from 'typesafe-actions';

declare module 'MyTypes' {
  export type Store = StateType<typeof import('./index').default>;
  export type RootAction = ActionType<typeof import('./root-action').default>;
  export type RootState = StateType<ReturnType<typeof import('./root-reducer').default>>;
}

declare module 'typesafe-actions' {
  interface Types {
    RootAction: ActionType<typeof import('./root-action').default>;
  }
}

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Create Store

When creating a store instance we don't need to provide any additional types. It will set-up a type-safe Store instance using type inference.

The resulting store instance methods like getState or dispatch will be type checked and will expose all type errors

import { RootAction, RootState, Services } from 'MyTypes';
import { createStore, applyMiddleware } from 'redux';
import { createEpicMiddleware } from 'redux-observable';
import { createBrowserHistory } from 'history';
import { routerMiddleware as createRouterMiddleware } from 'connected-react-router';

import { composeEnhancers } from './utils';
import rootReducer from './root-reducer';
import rootEpic from './root-epic';
import services from '../services';

// browser history
export const history = createBrowserHistory();

export const epicMiddleware = createEpicMiddleware<
  RootAction,
  RootAction,
  RootState,
  Services
>({
  dependencies: services,
});

const routerMiddleware = createRouterMiddleware(history);

// configure middlewares
const middlewares = [epicMiddleware, routerMiddleware];
// compose enhancers
const enhancer = composeEnhancers(applyMiddleware(...middlewares));

// rehydrate state on app start
const initialState = {};

// create store
const store = createStore(rootReducer(history), initialState, enhancer);

epicMiddleware.run(rootEpic);

// export store singleton instance
export default store;

---

Action Creators 

We'll be using a battle-tested helper library typesafe-actions   that's designed to make it easy and fun working with Redux in TypeScript.

To learn more please check this in-depth tutorial: Typesafe-Actions - Tutorial!

A solution below is using a simple factory function to automate the creation of type-safe action creators. The goal is to decrease maintenance effort and reduce code repetition of type annotations for actions and creators. The result is completely typesafe action-creators and their actions.

/* eslint-disable */
import { action } from 'typesafe-actions';

import { ADD, INCREMENT } from './constants';

/* SIMPLE API */

export const increment = () => action(INCREMENT);
export const add = (amount: number) => action(ADD, amount);

/* ADVANCED API */

// More flexible allowing to create complex actions more easily
// use can use "action-creator" instance in place of "type constant"
// e.g. case getType(increment): return action.payload;
// This will allow to completely eliminate need for "constants" in your application, more info here:
// https://github.com/piotrwitek/typesafe-actions#constants

import { createAction } from 'typesafe-actions';
import { Todo } from '../todos/models';

export const emptyAction = createAction(INCREMENT)<void>();
export const payloadAction = createAction(ADD)<number>();
export const payloadMetaAction = createAction(ADD)<number, string>();

export const payloadCreatorAction = createAction(
  'TOGGLE_TODO',
  (todo: Todo) => todo.id
)<string>();

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---

Reducers

State with Type-level Immutability

Declare reducer State type with readonly modifier to get compile time immutability

export type State = {
  readonly counter: number;
  readonly todos: ReadonlyArray<string>;
};

Readonly modifier allow initialization, but will not allow reassignment by highlighting compiler errors

export const initialState: State = {
  counter: 0,
}; // OK

initialState.counter = 3; // TS Error: cannot be mutated

It's great for Arrays in JS because it will error when using mutator methods like (push, pop, splice, ...), but it'll still allow immutable methods like (concat, map, slice,...).

state.todos.push('Learn about tagged union types') // TS Error: Property 'push' does not exist on type 'ReadonlyArray<string>'
const newTodos = state.todos.concat('Learn about tagged union types') // OK

Caveat - Readonly is not recursive

This means that the readonly modifier doesn't propagate immutability down the nested structure of objects. You'll need to mark each property on each level explicitly.

TIP: use Readonly or ReadonlyArray Mapped types

export type State = Readonly<{
  counterPairs: ReadonlyArray<Readonly<{
    immutableCounter1: number,
    immutableCounter2: number,
  }>>,
}>;

state.counterPairs[0] = { immutableCounter1: 1, immutableCounter2: 1 }; // TS Error: cannot be mutated
state.counterPairs[0].immutableCounter1 = 1; // TS Error: cannot be mutated
state.counterPairs[0].immutableCounter2 = 1; // TS Error: cannot be mutated

Solution - recursive Readonly is called DeepReadonly

To fix this we can use DeepReadonly type (available from utility-types).

import { DeepReadonly } from 'utility-types';

export type State = DeepReadonly<{
  containerObject: {
    innerValue: number,
    numbers: number[],
  }
}>;

state.containerObject = { innerValue: 1 }; // TS Error: cannot be mutated
state.containerObject.innerValue = 1; // TS Error: cannot be mutated
state.containerObject.numbers.push(1); // TS Error: cannot use mutator methods

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Typing reducer

to understand following section make sure to learn about Type Inference, Control flow analysis and Tagged union types

import { combineReducers } from 'redux';
import { ActionType } from 'typesafe-actions';

import { Todo, TodosFilter } from './models';
import * as actions from './actions';
import { ADD, CHANGE_FILTER, TOGGLE } from './constants';

export type TodosAction = ActionType<typeof actions>;

export type TodosState = Readonly<{
  todos: Todo[];
  todosFilter: TodosFilter;
}>;
const initialState: TodosState = {
  todos: [],
  todosFilter: TodosFilter.All,
};

export default combineReducers<TodosState, TodosAction>({
  todos: (state = initialState.todos, action) => {
    switch (action.type) {
      case ADD:
        return [...state, action.payload];

      case TOGGLE:
        return state.map(item =>
          item.id === action.payload
            ? { ...item, completed: !item.completed }
            : item
        );

      default:
        return state;
    }
  },
  todosFilter: (state = initialState.todosFilter, action) => {
    switch (action.type) {
      case CHANGE_FILTER:
        return action.payload;

      default:
        return state;
    }
  },
});

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Typing reducer with typesafe-actions

Notice we are not required to use any generic type parameter in the API. Try to compare it with regular reducer as they are equivalent.

import { combineReducers } from 'redux';
import { createReducer } from 'typesafe-actions';

import { Todo, TodosFilter } from './models';
import { ADD, CHANGE_FILTER, TOGGLE } from './constants';

export type TodosState = Readonly<{
  todos: Todo[];
  todosFilter: TodosFilter;
}>;
const initialState: TodosState = {
  todos: [],
  todosFilter: TodosFilter.All,
};

const todos = createReducer(initialState.todos)
  .handleType(ADD, (state, action) => [...state, action.payload])
  .handleType(TOGGLE, (state, action) =>
    state.map(item =>
      item.id === action.payload
        ? { ...item, completed: !item.completed }
        : item
    )
  );

const todosFilter = createReducer(initialState.todosFilter).handleType(
  CHANGE_FILTER,
  (state, action) => action.payload
);

export default combineReducers({
  todos,
  todosFilter,
});

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Testing reducer

import {
  todosReducer as reducer,
  todosActions as actions,
  TodosState,
} from './';

/**
 * FIXTURES
 */
const getInitialState = (initial?: Partial<TodosState>) =>
  reducer(initial as TodosState, {} as any);

/**
 * STORIES
 */
describe('Todos Stories', () => {
  describe('initial state', () => {
    it('should match a snapshot', () => {
      const initialState = getInitialState();
      expect(initialState).toMatchSnapshot();
    });
  });

  describe('adding todos', () => {
    it('should add a new todo as the first element', () => {
      const initialState = getInitialState();
      expect(initialState.todos).toHaveLength(0);
      const state = reducer(initialState, actions.add('new todo'));
      expect(state.todos).toHaveLength(1);
      expect(state.todos[0].title).toEqual('new todo');
    });
  });

  describe('toggling completion state', () => {
    it('should mark active todo as complete', () => {
      const activeTodo = { id: '1', completed: false, title: 'active todo' };
      const initialState = getInitialState({ todos: [activeTodo] });
      expect(initialState.todos[0].completed).toBeFalsy();
      const state1 = reducer(initialState, actions.toggle(activeTodo.id));
      expect(state1.todos[0].completed).toBeTruthy();
    });
  });
});

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---

Async Flow with redux-observable

Typing epics

import { RootAction, RootState, Services } from 'MyTypes';
import { Epic } from 'redux-observable';
import { tap, ignoreElements, filter } from 'rxjs/operators';
import { isOfType } from 'typesafe-actions';

import { todosConstants } from '../todos';

// contrived example!!!
export const logAddAction: Epic<RootAction, RootAction, RootState, Services> = (
  action$,
  state$,
  { logger }
) =>
  action$.pipe(
    filter(isOfType(todosConstants.ADD)), // action is narrowed to: { type: "ADD_TODO"; payload: string; }
    tap(action => {
      logger.log(
        `action type must be equal: ${todosConstants.ADD} === ${action.type}`
      );
    }),
    ignoreElements()
  );

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Testing epics

import { StateObservable, ActionsObservable } from 'redux-observable';
import { RootState, Services, RootAction } from 'MyTypes';
import { Subject } from 'rxjs';

import { add } from './actions';
import { logAddAction } from './epics';

// Simple typesafe mock of all the services, you dont't need to mock anything else
// It is decoupled and reusable for all your tests, just put it in a separate file
const services = {
  logger: {
    log: jest.fn<Services['logger']['log']>(),
  },
  localStorage: {
    loadState: jest.fn<Services['localStorage']['loadState']>(),
    saveState: jest.fn<Services['localStorage']['saveState']>(),
  },
};

describe('Todos Epics', () => {
  let state$: StateObservable<RootState>;

  beforeEach(() => {
    state$ = new StateObservable<RootState>(
      new Subject<RootState>(),
      undefined as any
    );
  });

  describe('logging todos actions', () => {
    beforeEach(() => {
      services.logger.log.mockClear();
    });

    it('should call the logger service when adding a new todo', done => {
      const addTodoAction = add('new todo');
      const action$ = ActionsObservable.of(addTodoAction);

      logAddAction(action$, state$, services)
        .toPromise()
        .then((outputAction: RootAction) => {
          expect(services.logger.log).toHaveBeenCalledTimes(1);
          expect(services.logger.log).toHaveBeenCalledWith(
            'action type must be equal: todos/ADD === todos/ADD'
          );
          // expect output undefined because we're using "ignoreElements" in epic
          expect(outputAction).toEqual(undefined);
          done();
        });
    });
  });
});

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---

Selectors with reselect

import { createSelector } from 'reselect';

import { TodosState } from './reducer';

export const getTodos = (state: TodosState) => state.todos;

export const getTodosFilter = (state: TodosState) => state.todosFilter;

export const getFilteredTodos = createSelector(getTodos, getTodosFilter, (todos, todosFilter) => {
  switch (todosFilter) {
    case 'completed':
      return todos.filter(t => t.completed);
    case 'active':
      return todos.filter(t => !t.completed);

    default:
      return todos;
  }
});

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---

Connect with react-redux

Typing connected component

NOTE: Below you'll find only a short explanation of concepts behind typing connect. For more real-world examples please check Redux Connected Components section.

import MyTypes from 'MyTypes';

import { bindActionCreators, Dispatch, ActionCreatorsMapObject } from 'redux';
import { connect } from 'react-redux';

import { countersActions } from '../features/counters';
import { FCCounter } from '../components';

// Type annotation for "state" argument is mandatory to check 
// the correct shape of state object and injected props you can also
// extend connected component Props interface by annotating `ownProps` argument
const mapStateToProps = (state: MyTypes.RootState, ownProps: FCCounterProps) => ({
  count: state.counters.reduxCounter,
});

// "dispatch" argument needs an annotation to check the correct shape
//  of an action object when using dispatch function
const mapDispatchToProps = (dispatch: Dispatch<MyTypes.RootAction>) =>
  bindActionCreators({
    onIncrement: countersActions.increment,
  }, dispatch);

// shorter alternative is to use an object instead of mapDispatchToProps function
const dispatchToProps = {
    onIncrement: countersActions.increment,
};

// Notice we don't need to pass any generic type parameters to neither
// the connect function below nor map functions declared above
// because type inference will infer types from arguments annotations automatically
// This is much cleaner and idiomatic approach
export const FCCounterConnected =
  connect(mapStateToProps, mapDispatchToProps)(FCCounter);

// You can add extra layer of validation of your action creators
// by using bindActionCreators generic type parameter and RootAction type
const mapDispatchToProps = (dispatch: Dispatch<MyTypes.RootAction>) =>
  bindActionCreators<ActionCreatorsMapObject<Types.RootAction>>({
    invalidActionCreator: () => 1, // Error: Type 'number' is not assignable to type '{ type: "todos/ADD"; payload: Todo; } | { ... }
  }, dispatch);

Typing connected component with redux-thunk integration

NOTE: When using thunk action creators you need to use bindActionCreators. Only this way you can get corrected dispatch props type signature like below.

WARNING: As of now (Apr 2019) bindActionCreators signature of the latest redux-thunk release will not work as below, you need to use updated type definitions that you can find here /playground/typings/redux-thunk/index.d.ts and then add paths overload in your tsconfig like this: "paths":{"redux-thunk":["typings/redux-thunk"]}.

const thunkAsyncAction = () => async (dispatch: Dispatch): Promise<void> => {
  // dispatch actions, return Promise, etc.
}

const mapDispatchToProps = (dispatch: Dispatch<Types.RootAction>) =>
  bindActionCreators(
    {
      thunkAsyncAction,
    },
    dispatch
  );

type DispatchProps = ReturnType<typeof mapDispatchToProps>;
// { thunkAsyncAction: () => Promise<void>; }

/* Without "bindActionCreators" fix signature will be the same as the original "unbound" thunk function: */
// { thunkAsyncAction: () => (dispatch: Dispatch<AnyAction>) => Promise<void>; }

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---

Configuration & Dev Tools

Common Npm Scripts

Common TS-related npm scripts shared across projects

"prettier": "prettier --list-different 'src/**/*.ts' || (echo '\nPlease fix code formatting by running:\nnpm run prettier:fix\n'; exit 1)",
"prettier:fix": "prettier --write 'src/**/*.ts'",
"lint": "tslint -p ./",
"tsc": "tsc -p ./ --noEmit",
"tsc:watch": "tsc -p ./ --noEmit -w",
"test": "jest --config jest.config.json",
"test:watch": "jest --config jest.config.json --watch",
"test:update": "jest --config jest.config.json -u"
"ci-check": "npm run prettier && npm run lint && npm run tsc && npm run test",

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tsconfig.json

We have our own recommended tsconfig.json that you can easily add to your project thanks to react-redux-typescript-scripts package.

Click to expand

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TSLib

https://www.npmjs.com/package/tslib

This library will cut down on your bundle size, thanks to using external runtime helpers instead of adding them per each file.

Installation
npm i tslib

Then add this to your tsconfig.json:

"compilerOptions": {
  "importHelpers": true
}

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TSLint

https://palantir.github.io/tslint/

Installation
npm i -D tslint

For React project you should add additional react specific rules: npm i -D tslint-react https://github.com/palantir/tslint-react

We have our own recommended config that you can easily add to your project thanks to react-redux-typescript-scripts package.

tslint.json

Click to expand

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ESLint

https://eslint.org/
https://typescript-eslint.io

Installation
npm i -D eslint @typescript-eslint/parser @typescript-eslint/eslint-plugin

We have our own recommended config that will automatically add a parser & plugin for TypeScript thanks to react-redux-typescript-scripts package.

.eslintrc

Click to expand

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Jest

https://jestjs.io/

Installation
npm i -D jest ts-jest @types/jest

jest.config.json

Click to expand

jest.stubs.js

Click to expand

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Style Guides

"react-styleguidist"

⟩⟩⟩ styleguide.config.js

⟩⟩⟩ demo

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---

Recipes

General Tips

- should I still use React.PropTypes in TS?

No. With TypeScript, using PropTypes is an unnecessary overhead. When declaring Props and State interfaces, you will get complete intellisense and design-time safety with static type checking. This way you'll be safe from runtime errors and you will save a lot of time on debugging. Additional benefit is an elegant and standardized method of documenting your component public API in the source code.

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- when to use interface declarations and when type aliases?

From practical side, using interface declaration will create an identity (interface name) in compiler errors, on the contrary type aliases doesn't create an identity and will be unwinded to show all the properties and nested types it consists of.
Although I prefer to use type most of the time there are some places this can become too noisy when reading compiler errors and that's why I like to leverage this distinction to hide some of not so important type details in errors using interfaces identity. Related ts-lint rule: https://palantir.github.io/tslint/rules/interface-over-type-literal/

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- what's better default or named exports?

A common flexible solution is to use module folder pattern, because you can leverage both named and default import when you see fit.
With this solution you'll achieve better encapsulation and be able to safely refactor internal naming and folders structure without breaking your consumer code:

// 1. create your component files (`select.tsx`) using default export in some folder:

// components/select.tsx
const Select: React.FC<Props> = (props) => {
...
export default Select;

// 2. in this folder create an `index.ts` file that will re-export components with named exports:

// components/index.ts
export { default as Select } from './select';
...

// 3. now you can import your components in both ways, with named export (better encapsulation) or using default export (internal access):

// containers/container.tsx
import { Select } from '@src/components';
or
import Select from '@src/components/select';
...

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- how to best initialize class instance or static properties?

Prefered modern syntax is to use class Property Initializers

class ClassCounterWithInitialCount extends React.Component<Props, State> {
  // default props using Property Initializers
  static defaultProps: DefaultProps = {
    className: 'default-class',
    initialCount: 0,
  };
  
  // initial state using Property Initializers
  state: State = {
    count: this.props.initialCount,
  };
  ...
}

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- how to best declare component handler functions?

Prefered modern syntax is to use Class Fields with arrow functions

class ClassCounter extends React.Component<Props, State> {
// handlers using Class Fields with arrow functions
  handleIncrement = () => {
    this.setState({ count: this.state.count + 1 });
  };
  ...
}

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Ambient Modules Tips

Imports in ambient modules

For type augmentation imports should stay outside of module declaration.

import { Operator } from 'rxjs/Operator';
import { Observable } from 'rxjs/Observable';

declare module 'rxjs/Subject' {
  interface Subject<T> {
    lift<R>(operator: Operator<T, R>): Observable<R>;
  }
}

When creating 3rd party type-definitions all the imports should be kept inside the module declaration, otherwise it will be treated as augmentation and show error

declare module "react-custom-scrollbars" {
    import * as React from "react";
    export interface positionValues {
    ...

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Type-Definitions Tips

Missing type-definitions error

if you cannot find types for a third-party module you can provide your own types or disable type-checking for this module using Shorthand Ambient Modules

// typings/modules.d.ts
declare module 'MyTypes';
declare module 'react-test-renderer';

Using custom d.ts files for npm modules

If you want to use an alternative (customized) type-definitions for some npm module (that usually comes with it's own type-definitions), you can do it by adding an override in paths compiler option.

{
  "compilerOptions": {
    "baseUrl": ".",
    "paths": {
      "redux": ["typings/redux"], // use an alternative type-definitions instead of the included one
      ...
    },
    ...,
  }
}

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Type Augmentation Tips

Strategies to fix issues coming from external type-definitions files (*.d.ts)

Augmenting library internal declarations - using relative import

// added missing autoFocus Prop on Input component in "antd@2.10.0" npm package
declare module '../node_modules/antd/lib/input/Input' {
  export interface InputProps {
    autoFocus?: boolean;
  }
}

Augmenting library public declarations - using node_modules import

// fixed broken public type-definitions in "rxjs@5.4.1" npm package
import { Operator } from 'rxjs/Operator';
import { Observable } from 'rxjs/Observable';

declare module 'rxjs/Subject' {
  interface Subject<T> {
    lift<R>(operator: Operator<T, R>): Observable<R>;
  }
}

More advanced scenarios for working with vendor type-definitions can be found here Official TypeScript Docs

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