srikanththyagarajan/react-redux-typescript-guide

The complete guide to static typing in "React & Redux" apps using TypeScript

React & Redux in TypeScript - Static Typing Guide

"This guide is a living compendium documenting the most important patterns and recipes on how to use React (and it's Ecosystem) in a functional style with TypeScript and to make your code completely type-safe while focusing on a conciseness of type annotations so it's a minimal effort to write and to maintain types in the long run."

To provide the best experience we focus on the symbiosis of type-safe complementary libraries and learning the concepts like Type Inference, Control flow analysis, Generics and some Advanced Types.

(Compatible with TypeScript v2.7.2)

Found it usefull? Want more updates? Give it a 🌟

Goals

• Complete type safety (with --strict flag) without loosing 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 redudancy 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

Playground Project

You should check Playground Project located in the /playground folder. It is a source of all the code examples found in the guide. They are all tested with the most recent version of TypeScript and 3rd party type definitions (like @types/react or @types/react-redux) to ensure the examples are up-to-date and not broken with updated definitions.

Playground was created is such a way, that you can simply clone the repository locally and immediately play around on your own to learn all the examples from this guide in a real project environment without the need to create some complicated environment setup by yourself.

---

Table of Contents

• Type Definitions & Complementary Libraries
• React Types Cheatsheet 🌟 NEW
• Component Typing Patterns
  • Stateless Components - SFC
  • Stateful Components - Class 📝 UPDATED
  • Generic Components
  • Render Props 🌟 NEW
  • Higher-Order Components 📝 UPDATED
  • Redux Connected Components
• Redux
  • Action Creators 📝 UPDATED
  • Reducers 📝 UPDATED
    • State with Type-level Immutability
    • Typing reducer
    • Testing reducer
  • Store Configuration 📝 UPDATED
  • Async Flow 📝 UPDATED
  • Selectors
• Tools
  • TSLint
  • Jest
  • Enzyme
  • Living Style Guide 🌟 NEW
  • Common Npm Scripts
• Recipes
  • tsconfig.json
  • Vendor Types Augmentation
  • Default and Named Module Exports
• FAQ
• Contribution Guide
• Project Examples
• Tutorials

---

Type Definitions & Complementary Libraries

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 from Redux v4.x.x (Beta). To make it work with Redux v3.x.x please refer to this config)

Complementary Libraries

Utility libraries with focus on type-safety providing a light functional abstractions for common use-cases

• "utility-types" - Utility Types for TypeScript (think lodash for types, moreover provides migration from Flow's Utility Types)
• "typesafe-actions" - Typesafe Action Creators for Redux / Flux Architectures (in TypeScript)

⇧ back to top

---

React Types Cheatsheet

React.StatelessComponent<P> or React.SFC<P>

Type representing stateless functional component

const MyComponent: React.SFC<MyComponentProps> = ...

⇧ back to top

React.Component<P, S>

Type representing statefull class component

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

⇧ back to top

React.ComponentType<P>

Type representing union type of (SFC | Component)

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

⇧ back to top

React.ReactElement<P> or JSX.Element

Type representing a concept of React Element - representation of a native DOM component (

), or a user-defined composite component ()

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

⇧ back to top

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 }) => ...

⇧ back to top

React.CSSProperties

Type representing style object in JSX (usefull for css-in-js styles)

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

⇧ back to top

React.ReactEventHandler<E>

Type representing generic event handler

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

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

⇧ back to top

React.MouseEvent<E> | React.KeyboardEvent<E> | React.TouchEvent<E> etc...

Type representing more specific event handler

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

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

⇧ back to top

---

Component Typing Patterns

Stateless Components - SFC

- stateless counter

import * as React from 'react';

export interface SFCCounterProps {
  label: string;
  count: number;
  onIncrement: () => any;
}

export const SFCCounter: React.SFC<SFCCounterProps> = (props) => {
  const { label, count, onIncrement } = props;

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

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

⟩⟩⟩ demo

⇧ back to top

- spread attributes link

import * as React from 'react';

export interface SFCSpreadAttributesProps {
  className?: string;
  style?: React.CSSProperties;
}

export const SFCSpreadAttributes: React.SFC<SFCSpreadAttributesProps> = (props) => {
  const { children, ...restProps } = props;

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

⟩⟩⟩ demo

⇧ back to top

---

Stateful Components - Class

- stateful counter

import * as React from 'react';

export interface StatefulCounterProps {
  label: string;
}

type State = {
  count: number;
};

export class StatefulCounter extends React.Component<StatefulCounterProps, State> {
  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>
    );
  }
}

⟩⟩⟩ demo

⇧ back to top

- with default props

import * as React from 'react';

export interface StatefulCounterWithDefaultProps {
  label: string;
  initialCount?: number;
}

interface DefaultProps {
  initialCount: number;
}

interface State {
  count: number;
}

export const StatefulCounterWithDefault: React.ComponentClass<StatefulCounterWithDefaultProps> =
  class extends React.Component<StatefulCounterWithDefaultProps & DefaultProps> {
    // to make defaultProps strictly typed we need to explicitly declare their type
    // @see https://github.com/DefinitelyTyped/DefinitelyTyped/issues/11640
    static defaultProps: DefaultProps = {
      initialCount: 0,
    };

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

    componentWillReceiveProps({ initialCount }: StatefulCounterWithDefaultProps) {
      if (initialCount != null && initialCount !== this.props.initialCount) {
        this.setState({ count: 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>
      );
    }
  };

⟩⟩⟩ demo

⇧ back to top

---

Generic Components

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

- generic list

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>
    );
  }
}

⟩⟩⟩ demo

⇧ back to top

---

Render Props

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

- name provider

simple component using children as a render prop

import * as React from 'react';

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

interface NameProviderState {
  name: string;
}

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

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

⟩⟩⟩ demo

⇧ back to top

- mouse provider

Mouse component found in Render Props React Docs

import * as React from 'react';

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

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

export class MouseProvider extends React.Component<MouseProviderProps, MouseProviderState> {
  state = { 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>
    );
  }
}

⟩⟩⟩ demo

⇧ back to top

---

Higher-Order Components

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

- withState

Adds state to a stateless counter

import * as React from 'react';
import { Subtract } from 'utility-types';

// These props will be subtracted from original component type
interface WrappedComponentProps {
  count: number;
  onIncrement: () => any;
}

export const withState = <P extends WrappedComponentProps>(
  WrappedComponent: React.ComponentType<P>
) => {
  // These props will be added to original component type
  interface Props {
    initialCount?: number;
  }
  interface State {
    count: number;
  }

  return class WithState extends React.Component<Subtract<P, WrappedComponentProps> & Props, State> {
    // Enhance component name for debugging and React-Dev-Tools
    static displayName = `withState(${WrappedComponent.name})`;

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

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

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

      return (
        <WrappedComponent
          {...remainingProps}
          count={count}
          onIncrement={this.handleIncrement}
        />
      );
    }
  };
};

show usage

import * as React from 'react';

import { withState } from '@src/hoc';
import { SFCCounter } from '@src/components';

const SFCCounterWithState =
  withState(SFCCounter);

export default (() => (
  <SFCCounterWithState label={'SFCCounterWithState'} />
)) as React.SFC<{}>;

⇧ back to top

- withErrorBoundary

Adds error handling using componentDidCatch to any component

import * as React from 'react';
import { Subtract } from 'utility-types';

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

interface WrappedComponentProps {
  onReset?: () => any;
}

export const withErrorBoundary = <P extends WrappedComponentProps>(
  WrappedComponent: React.ComponentType<P>
) => {
  interface Props { }
  interface State {
    error: Error | null | undefined;
  }

  return class WithErrorBoundary extends React.Component<Subtract<P, WrappedComponentProps> & Props, State> {
    static displayName = `withErrorBoundary(${WrappedComponent.name})`;

    state: State = {
      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 cloud
    }

    handleReset = () => {
      this.setState({ error: undefined });
    }

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

      if (error) {
        return (
          <WrappedComponent
            {...remainingProps}
            onReset={this.handleReset}
          />
        );
      }

      return children;
    }
  };
};

show usage

import * as React from 'react';

import { withErrorBoundary } from '@src/hoc';
import { ErrorMessage } from '@src/components';

const ErrorMessageWithErrorBoundary =
  withErrorBoundary(ErrorMessage);

const ErrorThrower = () => (
  <button type="button" onClick={() => { throw new Error(`Catch this!`); }}>
    {`Throw nasty error`}
  </button >
);

export default (() => (
  <ErrorMessageWithErrorBoundary>
    <ErrorThrower />
  </ErrorMessageWithErrorBoundary>
)) as React.SFC<{}>;

⇧ back to top

---

Redux Connected Components

Caveat with bindActionCreators

If you try to use connect or bindActionCreators explicitly and want to type your component callback props as () => void this will raise compiler errors. It happens because bindActionCreators typings will not map the return type of action creators to void, due to a current TypeScript limitations.

A decent alternative I can recommend is to use () => any type, it will work just fine in all possible scenarios and should not cause any typing problems whatsoever. All the code examples in the Guide with connect are also using this pattern.

If there is any progress or fix in regard to the above caveat I'll update the guide and make an announcement on my twitter/medium (There are a few existing proposals already).

There is alternative way to retain type soundness but it requires an explicit wrapping with dispatch and will be very tedious for the long run. See example below:

const mapDispatchToProps = (dispatch: Dispatch) => ({
  onIncrement: () => dispatch(actions.increment()),
});

- redux connected counter

import { connect } from 'react-redux';

import { RootState } from '@src/redux';
import { countersActions, countersSelectors } from '@src/redux/counters';
import { SFCCounter } from '@src/components';

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

export const SFCCounterConnected = connect(mapStateToProps, {
  onIncrement: countersActions.increment,
})(SFCCounter);

show usage

import * as React from 'react';

import { SFCCounterConnected } from '@src/connected';

export default () => (
  <SFCCounterConnected
    label={'SFCCounterConnected'}
  />
);

⇧ back to top

- redux connected counter (verbose)

import { bindActionCreators } from 'redux';
import { connect } from 'react-redux';

import { RootState, Dispatch } from '@src/redux';
import { countersActions } from '@src/redux/counters';
import { SFCCounter } from '@src/components';

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

const mapDispatchToProps = (dispatch: Dispatch) => bindActionCreators({
  onIncrement: countersActions.increment,
}, dispatch);

export const SFCCounterConnectedVerbose =
  connect(mapStateToProps, mapDispatchToProps)(SFCCounter);

show usage

import * as React from 'react';

import { SFCCounterConnectedVerbose } from '@src/connected';

export default () => (
  <SFCCounterConnectedVerbose
    label={'SFCCounterConnectedVerbose'}
  />
);

⇧ back to top

- with own props

import { connect } from 'react-redux';

import { RootState } from '@src/redux';
import { countersActions, countersSelectors } from '@src/redux/counters';
import { SFCCounter } from '@src/components';

export interface SFCCounterConnectedExtended {
  initialCount: number;
}

const mapStateToProps = (state: RootState, ownProps: SFCCounterConnectedExtended) => ({
  count: countersSelectors.getReduxCounter(state) + ownProps.initialCount,
});

export const SFCCounterConnectedExtended = connect(mapStateToProps, {
  onIncrement: countersActions.increment,
})(SFCCounter);

show usage

import * as React from 'react';

import { SFCCounterConnectedExtended } from '@src/connected';

export default () => (
  <SFCCounterConnectedExtended
    label={'SFCCounterConnectedExtended'}
    initialCount={10}
  />
);

⇧ back to top

---

Redux

Action Creators

Using Typesafe Action Creators helpers for Redux typesafe-actions

A recommended approach is to use a simple functional helper to automate the creation of type-safe action creators. The advantage is that we can reduce a lot of code repetition and also minimize surface of errors by using type-checked API.

There are more specialized functional helpers available that will help you to further reduce tedious boilerplate and type-annotations in common scenarios like reducers (using getType) or epics (using isActionOf).
All that without losing type-safety! Please check this very short Tutorial

import { createAction } from 'typesafe-actions';

export const countersActions = {
  increment: createAction('INCREMENT'),
  add: createAction('ADD', (amount: number) => ({
    type: 'ADD',
    payload: amount,
  })),
};

show usage

import store from '@src/store';
import { countersActions } from '@src/redux/counters';

// store.dispatch(countersActions.increment(1)); // Error: Expected 0 arguments, but got 1.
store.dispatch(countersActions.increment()); // OK => { type: "INCREMENT" }

⇧ back to top

---

Reducers

State with Type-level Immutability

Declare reducer State type with readonly modifier to get "type level" immutability

export type State = {
  readonly counter: number,
};

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

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

initialState.counter = 3; // Error, cannot be mutated

Caveat: Readonly does not provide a recursive immutability on objects

This means that the readonly modifier doesn't propagate immutability down to "properties" of objects. You'll need to set it explicitly on each nested property that you want.

Check the example below:

export type State = {
  readonly containerObject: {
    readonly immutableProp: number,
    mutableProp: number,
  }
};

state.containerObject = { mutableProp: 1 }; // Error, cannot be mutated
state.containerObject.immutableProp = 1; // Error, cannot be mutated

state.containerObject.mutableProp = 1; // OK! No error, can be mutated

Best-practices for nested immutability

use Readonly or ReadonlyArray Mapped types

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

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

There is a new (work in progress) feature called Conditional Types, that will allow ReadonlyRecursive mapped type

⇧ back to top

Typing reducer

using type inference with Discriminated Union types

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

import { ITodo, ITodosFilter } from './types';
import { addTodo, toggleTodo, changeFilter } from './actions';

export type TodosState = {
  readonly isFetching: boolean;
  readonly errorMessage: string | null;
  readonly todos: ITodo[];
  readonly todosFilter: ITodosFilter;
};

export type RootState = {
  todos: TodosState;
};

export const todosReducer = combineReducers<TodosState, TodosAction>({
  isFetching: (state = false, action) => {
    switch (action.type) {
      default: return state;
    }
  },
  errorMessage: (state = '', action) => {
    switch (action.type) {
      default: return state;
    }
  },
  todos: (state = [], action) => {
    switch (action.type) {
      case getType(addTodo):
        return [...state, action.payload];

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

      default: return state;
    }
  },
  todosFilter: (state = '', action) => {
    switch (action.type) {
      case getType(changeFilter):
        return action.payload;

      default: return state;
    }
  },
});

// inferring union type of actions
import { $call } from 'utility-types';
import * as actions from './actions';
const returnsOfActions = Object.values(actions).map($call);
export type TodosAction = typeof returnsOfActions[number];

⇧ back to top

Testing reducer

import { todosReducer, TodosState, TodosAction } from './reducer';
import { addTodo, changeFilter, toggleTodo } from './actions';

/**
 * FIXTURES
 */
const activeTodo = { id: '1', completed: false, title: 'active todo' };
const completedTodo = { id: '2', completed: true, title: 'completed todo' };

const initialState = todosReducer(undefined, {});

/**
 * SCENARIOS
 */
describe('Todos Logic', () => {

  describe('initial state', () => {
    it('should match a snapshot', () => {
      expect(initialState).toMatchSnapshot();
    });
  });

  describe('adding todos', () => {
    it('should add a new todo as the first active element', () => {
      const action = addTodo('new todo');
      const state = todosReducer(initialState, action);
      expect(state.todos).toHaveLength(1);
      expect(state.todos[0].id).toEqual(action.payload.id);
    });
  });

  describe('toggling completion state', () => {
    it('should mark as complete todo with id "1"', () => {
      const action = toggleTodo(activeTodo.id);
      const state0 = { ...initialState, todos: [activeTodo] };
      expect(state0.todos[0].completed).toBeFalsy();
      const state1 = todosReducer(state0, action);
      expect(state1.todos[0].completed).toBeTruthy();
    });
  });

});

⇧ back to top

---

Store Configuration

Create Root State and Root Action Types

RootState - interface representing redux state tree

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

import { combineReducers } from 'redux';
import { routerReducer, RouterState } from 'react-router-redux';

import { countersReducer, CountersState } from '@src/redux/counters';
import { todosReducer, TodosState } from '@src/redux/todos';

interface StoreEnhancerState { }

export interface RootState extends StoreEnhancerState {
  router: RouterState;
  counters: CountersState;
  todos: TodosState;
}

import { RootAction } from '@src/redux';
export const rootReducer = combineReducers<RootState, RootAction>({
  router: routerReducer,
  counters: countersReducer,
  todos: todosReducer,
});

⇧ back to top

RootAction - union type of all action objects

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

// RootActions
import { RouterAction, LocationChangeAction } from 'react-router-redux';
import { $call } from 'utility-types';

import { countersActions } from '@src/redux/counters';
import { todosActions } from '@src/redux/todos';
import { toastsActions } from '@src/redux/toasts';

const returnsOfActions = [
  ...Object.values(countersActions),
  ...Object.values(todosActions),
  ...Object.values(toastsActions),
].map($call);

type AppAction = typeof returnsOfActions[number];
type ReactRouterAction = RouterAction | LocationChangeAction;

export type RootAction =
  | AppAction
  | ReactRouterAction;

⇧ back to top

Create Store

When creating the store, use rootReducer. This will set-up a strongly typed Store instance with type inference.

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

import { createStore, applyMiddleware, compose } from 'redux';
import { createEpicMiddleware } from 'redux-observable';
import { rootReducer, rootEpic, RootState } from '@src/redux';

const composeEnhancers = (
  process.env.NODE_ENV === 'development' &&
  window && window.__REDUX_DEVTOOLS_EXTENSION_COMPOSE__
) || compose;

function configureStore(initialState?: RootState) {
  // configure middlewares
  const middlewares = [
    createEpicMiddleware(rootEpic),
  ];
  // compose enhancers
  const enhancer = composeEnhancers(
    applyMiddleware(...middlewares)
  );
  // create store
  return createStore(
    rootReducer,
    initialState!,
    enhancer
  );
}

// pass an optional param to rehydrate state on app start
const store = configureStore();

// export store singleton instance
export default store;

---

Async Flow

"redux-observable"

Use isActionOf helper to filter actions and to narrow RootAction union type to a specific "action type" down the stream.

import { combineEpics, Epic } from 'redux-observable';
import { isActionOf } from 'typesafe-actions';
import { Observable } from 'rxjs/Observable';
import cuid from 'cuid';

import { RootAction, RootState } from '@src/redux';
import { todosActions } from '@src/redux/todos';
import { toastsActions } from './';

const TOAST_LIFETIME = 2000;

const addTodoToast: Epic<RootAction, RootState> =
  (action$, store) => action$
    .filter(isActionOf(todosActions.addTodo))
    .concatMap((action) => { // action is type: { type: "ADD_TODO"; payload: string; }
      const toast = { id: cuid(), text: action.payload.title };

      const addToast$ = Observable.of(toastsActions.addToast(toast));
      const removeToast$ = Observable.of(toastsActions.removeToast(toast.id))
        .delay(TOAST_LIFETIME);

      return addToast$.concat(removeToast$);
    });

export const epics = combineEpics(addTodoToast);

⇧ back to top

---

Selectors

"reselect"

import { createSelector } from 'reselect';

import { RootState } from '@src/redux';

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

export const getTodosFilter =
  (state: RootState) => state.todos.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;
    }
  },
);

⇧ back to top

---

Action Creators - Alternative Pattern

This pattern is focused on a KISS principle - to stay clear of abstractions and to follow a more complex but familiar JavaScript "const" based approach:

Advantages:

• familiar to standard JS "const" based approach

Disadvantages:

• significant amount of boilerplate and duplication
• more complex compared to createAction helper library
• necessary to export both action types and action creators to re-use in other places, e.g. redux-saga or redux-observable

export const INCREMENT = 'INCREMENT'; 
export const ADD = 'ADD'; 

export type Actions = { 
  INCREMENT: { 
    type: typeof INCREMENT, 
  }, 
  ADD: { 
    type: typeof ADD,
    payload: number, 
  }, 
};

export type RootAction = Actions[keyof Actions];

export const actions = { 
  increment: (): Actions[typeof INCREMENT] => ({ 
    type: INCREMENT, 
  }), 
  add: (amount: number): Actions[typeof ADD] => ({ 
    type: ADD,
    payload: amount,
  }),
};

⇧ back to top

---

Tools

TSLint

Installation
npm i -D tslint

tslint.json

• Recommended setup is to extend build-in preset tslint:recommended (use tslint:all to enable all rules)
• Add additional react specific rules: npm i -D tslint-react https://github.com/palantir/tslint-react
• Overwritten some defaults for more flexibility

{
  "extends": ["tslint:recommended", "tslint-react"],
  "rules": {
    "arrow-parens": false,
    "arrow-return-shorthand": [false],
    "comment-format": [true, "check-space"],
    "import-blacklist": [true, "rxjs"],
    "interface-over-type-literal": false,
    "interface-name": false,
    "max-line-length": [true, 120],
    "member-access": false,
    "member-ordering": [true, { "order": "fields-first" }],
    "newline-before-return": false,
    "no-any": false,
    "no-empty-interface": false,
    "no-import-side-effect": [true],
    "no-inferrable-types": [true, "ignore-params", "ignore-properties"],
    "no-invalid-this": [true, "check-function-in-method"],
    "no-null-keyword": false,
    "no-require-imports": false,
    "no-submodule-imports": [true, "@src", "rxjs"],
    "no-this-assignment": [true, { "allow-destructuring": true }],
    "no-trailing-whitespace": true,
    "no-unused-variable": [true, "react"],
    "object-literal-sort-keys": false,
    "object-literal-shorthand": false,
    "one-variable-per-declaration": [false],
    "only-arrow-functions": [true, "allow-declarations"],
    "ordered-imports": [false],
    "prefer-method-signature": false,
    "prefer-template": [true, "allow-single-concat"],
    "quotemark": [true, "single", "jsx-double"],
    "semicolon": [true, "always"],
    "trailing-comma": [true, {
      "singleline": "never",
      "multiline": {
        "objects": "always",
        "arrays": "always",
        "functions": "never",
        "typeLiterals": "ignore"
      },
      "esSpecCompliant": true
    }],
    "triple-equals": [true, "allow-null-check"],
    "type-literal-delimiter": true,
    "typedef": [true,"parameter", "property-declaration"],
    "variable-name": [true, "ban-keywords", "check-format", "allow-pascal-case", "allow-leading-underscore"],
    // tslint-react
    "jsx-no-lambda": false
  }
}

⇧ back to top

Jest

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

jest.config.json

{
  "verbose": true,
  "transform": {
    ".(ts|tsx)": "./node_modules/ts-jest/preprocessor.js"
  },
  "testRegex": "(/spec/.*|\\.(test|spec))\\.(ts|tsx|js)$",
  "moduleFileExtensions": ["ts", "tsx", "js"],
  "moduleNameMapper": {
    "^Components/(.*)": "./src/components/$1"
  },
  "globals": {
    "window": {},
    "ts-jest": {
      "tsConfigFile": "./tsconfig.json"
    }
  },
  "setupFiles": [
    "./jest.stubs.js"
  ],
  "setupTestFrameworkScriptFile": "./jest.tests.js"
}

jest.stubs.js

// Global/Window object Stubs for Jest
window.requestAnimationFrame = function (callback) {
  setTimeout(callback);
};

window.localStorage = {
  getItem: function () { },
  setItem: function () { },
};

Object.values = () => [];

⇧ back to top

Enzyme

Installation
npm i -D enzyme enzyme-adapter-react-16 @types/enzyme

jest.tests.js

import { configure } from 'enzyme';
import Adapter from 'enzyme-adapter-react-16';

configure({ adapter: new Adapter() });

⇧ back to top

Living Style Guide

"react-styleguidist"

⟩⟩⟩ styleguide.config.js

⟩⟩⟩ demo

⇧ back to top

Common Npm Scripts

Common TS-related npm scripts shared across projects

"lint": "tslint -p ./",
"tsc": "tsc -p ./ --noEmit",
"tsc:watch": "tsc -p ./ --noEmit -w",
"pretest": "npm run lint & npm run tsc",
"test": "jest --config jest.config.json",
"test:watch": "jest --config jest.config.json --watch",
"test:update": "jest --config jest.config.json -u",

⇧ back to top

---

Recipes

tsconfig.json

• Recommended setup for best benefits from type-checking, with support for JSX and ES2016 features
• Add tslib to minimize bundle size: npm i tslib - this will externalize helper functions generated by transpiler and otherwise inlined in your modules
• Include absolute imports config working with Webpack

{
  "compilerOptions": {
    "baseUrl": "./", // enables absolute path imports
    "paths": { // define absolute path mappings
      "@src/*": ["src/*"] // will enable -> import { ... } from '@src/components'
      // in webpack you need to add -> resolve: { alias: { '@src': PATH_TO_SRC } }
    },
    "outDir": "dist/", // target for compiled files
    "allowSyntheticDefaultImports": true, // no errors on commonjs default import
    "allowJs": true, // include js files
    "checkJs": true, // typecheck js files
    "declaration": false, // don't emit declarations
    "emitDecoratorMetadata": true,
    "experimentalDecorators": true,
    "forceConsistentCasingInFileNames": true,
    "importHelpers": true, // importing helper functions from tslib
    "noEmitHelpers": true, // disable emitting inline helper functions
    "jsx": "react", // process JSX
    "lib": [
      "dom",
      "es2016",
      "es2017.object"
    ],
    "target": "es5", // "es2015" for ES6+ engines
    "module": "commonjs", // "es2015" for tree-shaking
    "moduleResolution": "node",
    "noEmitOnError": true,
    "noFallthroughCasesInSwitch": true,
    "noImplicitAny": true,
    "noImplicitReturns": true,
    "noImplicitThis": true,
    "noUnusedLocals": true,
    "strict": true,
    "pretty": true,
    "removeComments": true,
    "sourceMap": true
  },
  "include": [
    "src/**/*"
  ],
  "exclude": [
    "node_modules",
    "src/**/*.spec.*"
  ]
}

⇧ back to top

Default and Named Module Exports

Most flexible solution is to use module folder pattern, because you can leverage both named and default import when you see fit.
Using this solution you'll achieve better encapsulation for internal structure/naming refactoring without breaking your consumer code:

// 1. in `components/` folder create component file (`select.tsx`) with default export:

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

// 2. in `components/` folder create `index.ts` file handling named imports:

// 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';
...

⇧ back to top

Vendor Types Augmentation

Strategies to fix issues coming from broken "vendor type declarations" files (*.d.ts)

Augmenting library internal type declarations - using relative import resolution

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

⇧ back to top

Augmenting library public type declarations - using node module import resolution

// fixed broken public type declaration in "[email protected]" 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>;
  }
}

⇧ back to top

To quick-fix missing type declarations for vendor modules you can "assert" a module type with any using Shorthand Ambient Modules

// @src/types/modules.d.ts
declare module 'react-test-renderer';
declare module 'enzyme';

More advanced scenarios for working with vendor module declarations can be found here Official TypeScript Docs

⇧ back to top

---

FAQ

- should I still use React.PropTypes in TS?

No. With TypeScript, using PropTypes is an unnecessary overhead. When declaring IProps and IState interfaces, you will get complete intellisense and compile-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 external API in the source code.

⇧ back to top

- when to use interface declarations and when type aliases?

From practical side, using interface declaration will display identity (interface name) in compiler errors, on the contrary type aliases will be unwinded to show all the properties and nested types it consists of. This can be a bit noisy when reading compiler errors and I like to leverage this distinction to hide some of not so important type details in errors
Related ts-lint rule: https://palantir.github.io/tslint/rules/interface-over-type-literal/

⇧ back to top

- how to best initialize class instance or static properties?

Prefered modern style is to use class Property Initializers

class StatefulCounterWithInitialCount 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,
  };
  ...
}

⇧ back to top

- how to best declare component handler functions?

Prefered modern style is to use Class Fields with arrow functions

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

⇧ back to top

---

Contribution Guide

• Don't edit README.md - it is built with generator script from separate .md files located in the /docs/markdown folder, edit them instead
• For code snippets, they are also injected by generator script from the source files located in the playground folder (this step make sure all examples are type-checked and linted), edit them instead

look for include directives in .md files that look like this: ::[example|usage]='../../playground/src/components/sfc-counter.tsx'::

Before opening PR please make sure to check:

# run linter in playground
yarn run lint

# run type-checking in playground
yarn run tsc

# re-generate `README.md` from repo root
sh ./generate.sh
# or
node ./generator/bin/generate-readme.js

⇧ back to top

---

Project Examples

https://github.com/piotrwitek/react-redux-typescript-webpack-starter

⇧ back to top

Tutorials

Curated list of relevant in-depth tutorials

Higher-Order Components:

• https://medium.com/@jrwebdev/react-higher-order-component-patterns-in-typescript-42278f7590fb

⇧ back to top