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.

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 method:

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 method:

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 method 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 = {};

function fooBarReducer(state: State = initialState, action: typeof both): 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 method 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 = {};

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 method 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 = {};

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

action

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

The action method 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 method 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 method can be passed a config. The config should be created using the empty, payload, props or fsa methods.

empty

function empty()

The empty method constructs the config for the action method. 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 method constructs the config for the action method. 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 method constructs the config for the action method. 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 method constructs the config for the action method. 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 method is similar to the payload method, 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 method, 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 method 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): 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;
  }
}

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 type to `typeof union(foo, 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 method 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 method creates a reducer function out of the combined, action-specific reducers specified in the array. The array should be populated with the results of calls to the on method.

The on method 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 = {};

const fooBarReducer = reducer<State>([
  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 }))
], initialState);

liucougar / ts-action