Ts-describe-action NPM

ts-describe-action

reduce redux boilerplate and leverage typescript safety

Installation

npm add ts-describe-action

Note: requires typescript version >= 2.8

Motivation

// typical redux boilerplate with typesctipt
const ADD_TODO = 'ADD_TODO';

type AddTodoAction = { type: typeof ADD_TODO; text: string };
const addTodo = (text: string): AddTodoAction => ({ type: ADD_TODO, text });

const TOGGLE_TODO = 'TOGGLE_TODO';

type ToggleTodoAction = { type: typeof TOGGLE_TODO; index: number };
const toggleTodo = (index: number): ToggleTodoAction => ({
  type: TOGGLE_TODO,
  index
});

type Todo = { text: string; completed: boolean };

function todosReducer(prev: Todo[] = [], action: Action): Todo[] {
  switch (action.type) {
    case ADD_TODO: {
      const { text } = <AddTodoAction>action;
      return [...prev, { text, completed: false }];
    }
    case TOGGLE_TODO: {
      const { index } = <ToggleTodoAction>action;
      return prev.map((todo, i) =>
        index === i ? { text: todo.text, completed: !todo.completed } : todo
      );
    }
    default:
      return state;
  }
}

// usage
dispatch(addTodo('reduce boilerplate'));
dispatch(toggleTodo(0));

Most of that is by design: we need to decouple intent & effect. But what if we rely on typescript to keep us honest but with less hassle?

The same code rewritten with this library

import { createReducer, describeAction } from 'ts-describe-action';

type Todo = { text: string; completed: boolean };

// return value is an action creator function with a couple extra properties
const addTodo = describeAction('ADD_TODO', (prev: Todo[], text: string) => [
  ...prev,
  { text, completed: false }
]);

const toggleTodo = describeAction(
  'TOGGLE_TODO',
  (prev: Todo[], index: number) =>
    prev.map((todo, i) =>
      index === i ? { text: todo.text, completed: !todo.completed } : todo
    )
);

// combines handlers into a single reducer function
const todosReducer = createReducer([addTodo, toggleTodo], [] /*initial state*/);

// usage as with normal action creators
// note that addTodo & toggleTodo are typesafe. Payload type is inferred
dispatch(addTodo('reduce boilerplate'));
dispatch(toggleTodo(0));

You don't have to rewrite anything in your existing code

The library is designed for gradual adoption. So you can use individual features independently from each other.

Using `isMine` typeguard and `handle` functions in your normal reducer

// normal action
const ADD_TODO = 'ADD_TODO';
type AddTodoAction = { type: typeof ADD_TODO; text: string };
const addTodo = (text: string): AddTodoAction => ({ type: ADD_TODO, text });

// newly declared action
const toggleTodo = describeAction(
  'TOGGLE_TODO',
  (prev: Todo[], index: number) =>
    prev.map((todo, i) =>
      index === i ? { text: todo.text, completed: !todo.completed } : todo
    )
);

// your normal reducer function
function todosReducer(state: Todo[] = [], action: Action): Todo[] {
  switch (action.type) {
    case ADD_TODO: {
      const { text } = <AddTodoAction>action;
      return [...prev, { text, completed: false }];
    }
    default: {
      if (toggleTodo.isMine(action)) {
        // here type of action.payload is number
        // note that type ('TOGGLE_TODO') is also available as toggleTodo.type
        return toggleTodo.handle(state, action.payload);
      }

      return state;
    }
  }
}

Old `create` function is still there

In the prev versions of the library the result of describeAction was an object with a property create that was an action creator.

Now the result of describeAction is a function that itself is an action creator but has all the same properties as before. Therefore backwards compatible.

const addTodo = describeAction('ADD_TODO', (prev: Todo[], text: string) => [
  ...prev,
  { text, completed: false }
]);

const add = addTodo('check new api');
// {type: 'ADD_TODO', payload: 'check new api'}

const add2 = addTodo.create('old api is still there');
// {type: 'ADD_TODO', payload: 'old api is still there'}

Supports actions with no payload

Just omit payload argument:

const increment = describeAction('Inc', (prev: number) => prev + 1);
const decrement = describeAction('Dec', (prev: number) => prev - 1);

// Doesn't require payload argument
const inc = increment(); // {type: 'Inc', payload: undefined}

//handler
const result = increment.handle(0); // result === 1

const reducer = createReducer([increment, decrement], 0);

Yet another typescript redux library?

I love redux but I hate writing boilerplate code. So I wanted an api that would have a small api surface yet would be useful regardless how you write your redux code. So my goals were:

collocate action tag, shape of payload and the way to handle the action. So I would look at exactly one place for any action related stuff.
do so with as little syntax as possible leveraging type inference.
small api surface and small bundle size.
make it useful for "brownfield" project. You can try to convert a small reducer function and go from there.
make it decomposable. So it's a collections of small pieces that work really nicely together rather than "one big thing". So it is still useful with or without other libraries (Ex: I use unionize to model state)

I was unable to find anything I really liked, so here you go.

API

There are two types of action descriptions:

// With payload
export interface ActionDesc<TType extends string, TState, TPayload> {
  // this is an action creator function
  (payload: TPayload): Action<TType, TPayload>;

  // literal type like 'ADD_TODO'
  type: TType;

  // the reducer function. Note that it takes payload not the action itself
  handle: (prev: TState, payload: TPayload) => TState;

  // this is for backward compatibility. ActionDesc used be just an object
  create: (payload: TPayload) => Action<TType, TPayload>;

  // typeguard for working with actions manually
  isMine: (action: AnyAction) => action is Action<TType, TPayload>;
}

// No payload
export interface ActionSimpleDesc<TType extends string, TState> {
  // this is an action creator function with no arguments
  (): Action<TType>;

  type: TType;
  handle: (prev: TState) => TState;
  create: () => Action<TType>;
  isMine: (action: AnyAction) => action is Action<TType>;
}

The API itself is just 2 functions:

// create action description
const describeAction: Describe;

type Describe = {
  <TType extends string, TState>(
    type: TType,
    handle: (prev: TState) => TState
  ): ActionSimpleDesc<TType, TState>;

  <TType extends string, TState, TPayload>(
    type: TType,
    handle: (prev: TState, payload: TPayload) => TState
  ): ActionDesc<TType, TState, TPayload>;
};

// combine all descriptions into one reducer
export function createReducer<TState>(
  descriptions: (
    | ActionDesc<string, TState, any>
    | ActionSimpleDesc<string, TState>)[],
  initialState: TState
): Reducer<TState>;