Solid Reducer

A simple reducer for SolidJS.

Inspired by React's useReducer hook, solid-reducer is a simple reducer for SolidJS.

Installation

npm i @jartur/solid-reducer

yarn add @jartur/solid-reducer

pnpm add @jartur/solid-reducer

Usage

Without explicit types:

import { createReducer } from "@jartur/solid-reducer";

const [store, dispatch] = createReducer(
  (set) => ({
    increment: () => set("count", (c) => c + 1),
    decrement: () => set("count", (c) => c - 1),
    setText: (payload: string) => set("text", payload),
  }),
  { count: 0, text: "" }
);

console.log(store); // { count: 0, text: "" }
dispatch("increment");
console.log(store); // { count: 1, text: "" }
dispatch("decrement");
console.log(store); // { count: 0, text: "" }
dispatch("setText", "foo");
console.log(store); // { count: 0, text: "foo" }

With explicit types:

import { Reducer, createReducer } from "@jartur/solid-reducer";

type Store = {
  count: number;
  text: string;
};

type ActionRecord = {
  increment: void;
  decrement: void;
  setText: string;
};

const reducer: Reducer<Store, ActionRecord> = (set) => ({
  increment: () => set("count", (c) => c + 1),
  decrement: () => set("count", (c) => c - 1),
  setText: (payload) => set("text", payload),
});

const [store, dispatch] = createReducer(reducer, { count: 0, text: "" });

console.log(store); // { count: 0, text: "" }
dispatch("increment");
console.log(store); // { count: 1, text: "" }
dispatch("decrement");
console.log(store); // { count: 0, text: "" }
dispatch("setText", "foo");
console.log(store); // { count: 0, text: "foo" }

API

createReducer

The createReducer function takes a reducer function and an initial value and returns a store and a dispatch function.

function createReducer<Store extends object, ActionRecord>(
  reducer: Reducer<Store, ActionRecord>,
  initialValue: Store
): [Store<Store>, Dispatcher<ActionRecord>];

Reducer

The reducer function is a setup function that takes a setStore function and a store and returns an object with action handlers.

Action handlers are just functions that take a payload to update the store.

type Reducer<Store, ActionRecord> = (
  setStore: SetStoreFunction<Store>,
  store: Store
) => ActionMap<ActionRecord>;

type ActionMap<ActionRecord> = {
  [Action in keyof ActionRecord]: void extends ActionRecord[Action]
    ? () => void
    : (payload: ActionRecord[Action]) => void;
};

setStore and store

The setStore function and the store object are from solid-js/store.

ActionRecord

The ActionRecord type is a record that maps action types to their payload types. Actions that do not have a payload are mapped to void.

dispatch

The dispatch function receives an action type and a payload and calls the corresponding action handler.

If the ActionRecord defines a payload of type void, there is no second argument.

export type DispatchFn<ActionRecord> = <ActionType extends keyof ActionRecord>(
  type: ActionType,
  ...[payload]: void extends ActionRecord[ActionType]
    ? []
    : [payload: ActionRecord[ActionType]]
) => void;

dispatch.subset

export type Dispatcher<ActionRecord> = DispatchFn<ActionRecord> & {
  subset: <Action extends keyof ActionRecord>(
    this: DispatchFn<ActionRecord>,
    actions: Action[]
  ) => SubDispatcher<ActionRecord, Action>;
};

export type SubDispatcher<
  ActionRecord,
  Action extends keyof ActionRecord
> = DispatchFn<Pick<ActionRecord, Action>> & {
  subset: <SubAction extends Action>(
    this: DispatchFn<Pick<ActionRecord, Action>>,
    actions: SubAction[]
  ) => SubDispatcher<ActionRecord, SubAction>;
};

The dispatch.subset function is a helper function that accepts an array of action types and returns a dispatch function that only accepts this defined subset of actions.

This is useful for passing dispatch functions to components that should only be able to dispatch a subset of actions.

Passing an action type that is not defined in the subset throws an error at runtime and a typescript error at compile time.

const [store, dispatch] = createReducer(reducer, { count: 0, text: "" });

const dispatchCount = dispatch.subset(["increment", "decrement"]);

dispatchCount("increment");
dispatchCount("decrement");
dispatchCount("setText"); // throws Error: 'Action "setText" not allowed from this dispatcher'
// Typescript Error: 'Argument of type "setText" is not assignable to parameter of type "increment" | "decrement"'.

The dispatch.subset function can be chained to create a subset from a subset with any depth.

const dispatchCount = dispatch.subset(["increment", "decrement"]);

const dispatchIncrement = dispatchCount.subset(["increment"]);

dispatchIncrement("increment");
dispatchIncrement("decrement"); // throws Error: 'Action "decrement" not allowed from this dispatcher'
// Typescript Error: 'Argument of type "decrement" is not assignable to parameter of type "increment"'.

If you want to pass a subset of actions to a component, you can use the subset function in the component's setup function.

const Component = () => {
  const [store, dispatch] = createReducer(reducer, { count: 0, text: "" });
  const dispatchCount = dispatch.subset(["increment", "decrement"]);

  return <Child dispatch={dispatchCount} />;
};

const Child = (props: {
  dispatch: SubDispatcher<ActionRecord, "increment" | "decrement">;
}) => {
  return <button onClick={() => props.dispatch("increment")}>Increment</button>;
};

If you want the type-safety of a subset, but not the runtime implications, you can just assign the dispatch function to a variable with a SubDispatcher type.

const [store, dispatch] = createReducer(reducer, { count: 0, text: "" });
const dispatchCount: SubDispatcher<ActionRecord, "increment" | "decrement"> =
  dispatch;

dispatchIncrement("increment");
dispatchIncrement("decrement");
dispatchIncrement("setText"); // does not throw Error at runtime
// Typescript Error: 'Argument of type "setText" is not assignable to parameter of type "increment" | "decrement"'.

You can use the SubDispatcher type on the props of a component to get type-safety and pass the full dispatch function directly.

const Component = () => {
  const [store, dispatch] = createReducer(reducer, { count: 0, text: "" });

  return <Child dispatch={dispatch} />;
};

const Child = (props: {
  dispatch: SubDispatcher<ActionRecord, "increment" | "decrement">;
}) => {
  return <button onClick={() => props.dispatch("increment")}>Increment</button>;
};

Store

Since createReducer is a wrapper around createStore, you can use produce, reconcile, unwrap, and anything else you can do with a regular store.

import { Reducer, createReducer } from "@jartur/solid-reducer";
import { produce, unwrap } from "solid-js/store";
import { ActionRecord, Store } from "./types";

const reducer: Reducer<Store, ActionRecord> = (set) => ({
  increment: () => set(produce((draft) => draft.count++)),
  decrement: () => set(produce((draft) => draft.count--)),
  setText: (payload) => set(produce((draft) => (draft.text = payload))),
});

const [store, dispatch] = createReducer(reducer, { count: 0, text: "" });

const data = unwrap(store);