ts-action

What is it?

ts-action is a package for declaring Redux action creators with less TypeScript cruft.

Why might you need it?

I wanted a mechanism for declaring and consuming actions that involved writing as little boilerplate as possible. If you, too, want less cruft, you might find this package useful.

Also, if you are using NgRx or redux-observable, you might find the ts-action-operators package useful, too - it includes an RxJS pipeable ofType operator that can be passed a ts-action action creator.

And there is an alternative implementation for the on function in ts-action-immer - which passed an Immer Draft as the reducer's state argument.

For an in-depth look at TypeScript, Redux and ts-action, have a look at: How to Reduce Action Boilerplate.

Install

Install the package using npm:

npm install ts-action --save

TypeScript version 3.0 or later is required.

Usage

Action creators are declared using the action function:

import { action } from "ts-action";
const foo = action("FOO");

Actions are created using the returned action creator function:

store.dispatch(foo());

For actions with payloads, the payload type is specified using the payload function:

import { action, payload } from "ts-action";
const foo = action("FOO", payload<{ foo: number }>());

and the payload value is specified when creating the action:

store.dispatch(foo({ foo: 42 }));

To have the properties added to the action itself - rather than a payload property - use the props function instead. Or, for more control over the parameters accepted by the action creator, pass a creator function.

Action creators have a type property that can be used to narrow an action's TypeScript type in a reducer.

The action types can be combined into a discriminated union and the action can be narrowed to a specific TypeScript type using a switch statement, like this:

import { action, payload, union } from "ts-action";

const foo = action("FOO", payload<{ foo: number }>());
const bar = action("BAR", payload<{ bar: number }>());
const both = union(foo, bar);

interface State { foo?: number; bar?: number; }
const initialState: State = {};

function fooBarReducer(state: State = initialState, action: typeof both.actions): State {
  switch (action.type) {
  case foo.type:
    return { ...state, foo: action.payload.foo };
  case bar.type:
    return { ...state, bar: action.payload.bar };
  default:
    return state;
  }
}

Or, the package's isType function can be used to narrow the action's type using if statements, like this:

import { action, isType, payload } from "ts-action";

const foo = action("FOO", payload<{ foo: number }>());
const bar = action("BAR", payload<{ bar: number }>());

interface State { foo?: number; bar?: number; }
const initialState: State = {};

function fooBarReducer(state: State = initialState, action: Action): State {
  if (isType(action, foo)) {
    return { ...state, foo: action.payload.foo };
  }
  if (isType(action, bar)) {
    return { ...state, bar: action.payload.bar };
  }
  return state;
}

Or, the package's reducer function can be used to create a reducer function, like this:

import { action, on, payload, reducer } from "ts-action";

const foo = action("FOO", payload<{ foo: number }>());
const bar = action("BAR", payload<{ bar: number }>());

interface State { foo?: number; bar?: number; }
const initialState: State = {};

const fooBarReducer = reducer(
  initialState,
  on(foo, (state, { payload }) => ({ ...state, foo: payload.foo })),
  on(bar, (state, { payload }) => ({ ...state, bar: payload.bar }))
);

API

• action
• empty
• payload
• fsa
• props
• creator
• union
• isType
• guard
• reducer

action

function action<T>(type: T)
function action<T>(type: T, config: unknown)
function action<T>(type: T, creator: (...args: any[]) => object)

The action function returns an action creator. Action creators are functions:

const foo = action("FOO");
const fooAction = foo();
console.log(fooAction); // { type: "FOO" }

The type argument passed to action must be a string literal or have a string-literal type. Otherwise, TypeScript will not be able to narrow actions in a discriminated union.

The type option passed to the action function can be obtained using the creator's static type property:

switch (action.type) {
case foo.type:
  return { ...state, foo: action.payload.foo };
default:
  return state;
}

To define propeties, the action function can be passed a config. The config should be created using the empty, payload, props or fsa functions.

empty

function empty()

The empty function constructs the config for the action function. To declare an action without a payload or properties , call it like this:

const foo = action("FOO", empty());
const fooAction = foo();
console.log(fooAction); // { type: "FOO" }

Actions default to being empty; if only a type is passed to the action call, an empty action is created by default:

const foo = action("FOO");
const fooAction = foo();
console.log(fooAction); // { type: "FOO" }

payload

function payload<T>()

The payload function constructs the config for the action function. To declare action properties within a payload property, call it like this:

const foo = action("FOO", payload<{ name: string }>());
const fooAction = foo({ name: "alice" });
console.log(fooAction); // { type: "FOO", payload: { name: "alice" } }

fsa

function fsa<T>()

The fsa function constructs the config for the action function. To declare action properties within a payload property, call it like this:

const foo = action("FOO", fsa<{ name: string }>());
const fooAction = foo({ name: "alice" });
console.log(fooAction); // { type: "FOO", payload: { name: "alice" }, error: false, meta: undefined }

The action creator returns a Flux Standard Action and can also be passed an Error instance:

const fooAction = foo(new Error("Kaboom!"));
console.log(fooAction); // { type: "FOO", payload: Error("Kaboom!"), error: true, meta: undefined }

props

function props<T>()

The props function constructs the config for the action function. To declare action properties at the same level as the type property, call it like this:

const foo = action("FOO", props<{ name: string }>());
const fooAction = foo({ name: "alice" });
console.log(fooAction); // { type: "FOO", name: "alice" }

The props function is similar to the payload function, but with props, the specified properties are added to the action itself - rather than a payload property.

creator

Instead of passing a config to the action function, a creator function can be passed like this:

const foo = action("FOO", (name: string) => ({ name }));
const fooAction = foo("alice");
console.log(fooAction); // { type: "FOO", name: "alice" }

Passing a creator function offers more control over property defaults, etc.

union

The union function can be used to infer a union of actions - for type narrowing using a discriminated union. It's passed action creators and returns a value that can be used with TypeScript's typeof operator, like this:

const both = union(foo, bar);
function reducer(state: any = [], action: typeof both.actions): any {
  switch (action.type) {
  case fFoo.type:
    return ... // Here the action will be narrowed to Foo.
  case bar.type:
    return ... // Here the action will be narrowed to Bar.
  default:
    return state;
  }
}

union can be used if more than three action creators need to be passed to on.

isType

isType is a TypeScript type guard that will return either true or false depending upon whether the passed action is of the appropriate type. TypeScript will narrow the type when used with an if statement.

For example:

if (isType(action, foo)) {
  // Here, TypeScript has narrowed the type, so the action is strongly typed
  // and individual properties can be accessed in a type-safe manner.
}

isType can also be passed multiple action creators:

if (isType(action, foo, bar)) {
  // Here, TypeScript has narrowed the action type to an action created
  // by foo or bar.
}

guard

guard is a higher-order equivalent of isType. That is, it returns a TypeScript type guard that will, in turn, return either true or false depending upon whether the passed action is of the appropriate type. The guard function is useful when dealing with APIs that accept type guards.

For example, Array.prototype.filter accepts a type guard:

const actions = [foo(), bar()];
const filtered = actions.filter(guard(foo));
// TypeScript will have narrowed the type of filtered, so the actions within
// the array are strongly typed and individual properties can be accessed in
// a type-safe manner.

guard can also be passed multiple action creators:

const actions = [foo(), bar(), baz()];
const filtered = actions.filter(guard(foo, bar));

reducer

The reducer function creates a reducer function out of the combined, action-specific reducers declared using the on function.

The on function creates a reducer for a specific, narrowed action and returns an object - containing the created reducer and the types of one or more action creators.

import { action, on, payload, reducer } from "ts-action";

const foo = action("FOO", payload<{ foo: number }>());
const bar = action("BAR", payload<{ bar: number }>());
const fooError = action("FOO_ERROR", payload<{ foo: number, error: {} }>());
const barError = action("BAR_ERROR", payload<{ bar: number, error: {} }>());

interface State { foo?: number; bar?: number; error?: {} }
const initialState: State = {};

const fooBarReducer = reducer(
  initialState,
  on(foo, (state, { payload }) => ({ ...state, foo: payload.foo })),
  on(bar, (state, { payload }) => ({ ...state, bar: payload.bar })),
  on(fooError, barError, (state, { payload }) => ({ ...state, error: payload.error }))
);

If more that three action creators need to be passed to on, you can use union, like this:

on(
  ...union(foo, bar, baz, boo),
  (state, { payload }) => /* whatever */
)