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.

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-dev

TypeScript version 2.6 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 action creator as a class:

store.dispatch(new Foo());

Although the actions are created as class instances, internally, the prototype is reset, so they are compatible with reactjs/redux, as they are considered to be plain objects.

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(new 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 constructor, use the base method.

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 } from "ts-action";

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

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

function fooBarReducer(state: State = initialState, action: typeof All): 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);

API

• action
• empty
• payload
• props
• base
• union
• isType
• guard
• reducer
• on

action

function action<T, C extends Ctor<{}>>(type: T, options?: { BaseCtor: C })

The action method returns an action creator. Action creators are classes and actions are be created using new:

const Foo = action("FOO");
const foo = new Foo();
console.log(foo); // { 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 options. The options should be created using the empty, payload, props or base methods.

empty

function empty()

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

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

payload

function payload<T>()

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

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

props

function props<T>()

The props method constructs options 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 foo = new Foo({ name: "alice" });
console.log(foo); // { 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.

base

function base<C extends Ctor<{}>>(BaseCtor: C)

The base method constructs options for the action method. To declare a base class with properties, call it like this:

const Foo = action("FOO", base(class { constructor(public name: string) {} }));
const foo = new Foo("alice");
console.log(foo); // { type: "FOO", name: "alice" }

The base method offers more control over property defaults, etc. as the base class is declared inline.

union

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

const All = union(Foo, Bar);
function reducer(state: any = [], action: typeof All): any {
  switch (action.type) {
  case Foo.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.
}

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 = [new Foo(), new Bar()];
const filtered = actions.filter(guard(Foo)); // Inferred to be: const filtered: Foo[]

reducer

function reducer<S>(
  ons: { reducer: Reducer<S>, type: string }[],
  initialState: S
): Reducer<S>;

The reducer method creates a reducer function out of the combined, action-specific reducers specified in the array.

on

function on<T extends string, A extends Action<string>, S>(
  creator: ActionCreator<T, A>,
  reducer: (state: S, action: A) => S
): { reducer: Reducer<S>, type: string };

The on method creates a reducer for a specific, narrowed action and returns an object - containing the created reducer and the action's type - that can be passed to the reducer method.