State Designer / React

This package includes the core functions of State Designer, a JavaScript state management library, together with a React hook for use in React. Click here to learn more.

You can use this package in any React project. For other JavaScript projects, see @state-designer/core.

This package includes TypeScript typings.

Installation

npm install @state-designer/react

yarn add @state-designer/react

Usage

You can use the useStateDesigner hook to subscribe to either a global state (created with the createState function) or a local component state, by passing a configuration object to the hook. You can use the useSelector hook to subscribe to only part of a state.

For the basics of State Designer (including the configuration object API) see the documentation for @state-designer/core or visit state-designer.com.

API

• useStateDesigner
• useSelector
• createSelector
• useUpdateEffect

---

useStateDesigner

const update = useStateDesigner(myState)

Subscribes a component to an state created with createState.

import { createState, useStateDesigner } from '@state-designer/react'

export const state = createState({
  data: { count: 0 },
  states: {
    enabled: {
      on: {
        INCREMENTED: { do: (data) => data.count++ },
        TOGGLED: { to: 'disabled' },
      },
    },
    disabled: {
      on: {
        TOGGLED: { to: 'enabled' },
      },
    },
  },
})

function Counter() {
  const local = useStateDesigner(state)
  return (
    <div>
      <button disabled={!state.can('INCREMENTED')} onClick={() => state.send('INCREMENTED')}>
        {local.data.count}
      </button>
      <button onClick={() => state.send('TOGGLED')}>Toggle</button>
    </div>
  )
}

Usage with a Configuration Object

const update = useStateDesigner(myState)

If given a configuration object, the hook will creates a new state and subscribe to it.

import { useStateDesigner } from '@state-designer/react'

function Counter() {
  const local = useStateDesigner({
    data: { count: 0 },
    states: {
      enabled: {
        on: {
          INCREMENTED: { do: (data) => data.count++ },
          TOGGLED: { to: 'disabled' },
        },
      },
      disabled: {
        on: {
          TOGGLED: { to: 'enabled' },
        },
      },
    },
  })

  return (
    <div>
      <button disabled={!state.can('INCREMENTED')} onClick={() => state.send('INCREMENTED')}>
        {local.data.count}
      </button>
      <button onClick={() => state.send('TOGGLED')}>Toggle</button>
    </div>
  )
}

Dependencies

When given a configration object, you may also provide an array of dependencies that will, if changed between renders, cause the component to create and subscribe to a new state based on the current configuration object.

import { useStateDesigner } from '@state-designer/react'

function Counter({ initial = 0 }) {
  const local = useStateDesigner(
    {
      data: { count: initial },
      on: { INCREMENTED: { do: (data) => data.count++ } },
    },
    [initial]
  )

  return (
    <div>
      <button onClick={() => state.send('INCREMENTED')}>{local.data.count}</button>
    </div>
  )
}

---

useSelector

const selected = useSelector(state, selectFn)

Subscribe to only certain changes from a state. Pass it a created state, together with a callback function that receives the update and returns some value. Whenever the state updates, the hook will update only if the value returned by your callback function has changed.

import { createState, useSelector } from '@state-designer/react'

const state = createState({
  data: {
    tables: 0,
    chairs: 0,
  },
  on: {
    ADDED_TABLE: (data) => data.tables++,
    ADDED_CHAIRS: (data) => data.chairs++,
  },
})

// This component will only update when state.data.tables changes.
function TablesCounter() {
  const tables = useSelector(state, (state) => state.data.tables)
  return <button onClick={() => state.send('ADDED_TABLE')}>{tables}</button>
}

// This component will only update when state.data.chairs changes.
function ChairsCounter() {
  const chairs = useSelector(state, (state) => state.data.chairs)
  return <button onClick={() => state.send('ADDED_CHAIR')}>{chairs}</button>
}

Comparisons

The hook will only update if the selector function returns new data. By default, the hook uses strict equality (a === b) to compare the previous data with the new data. However, the hook also accepts an optional third argument: a callback function that it will use for comparisons instead.

Each time the state updates, the hook will use the selection function to make a new selection, then call the comparison function with two arguments: the selection currently in state (the "previous" selection) and the new selection just obtained. If the comparison function returns false, then the hook will put the new selection into state.

const tooMany = useSelector(
  state,
  (state) => state.data.chairs,
  (prev, next) => prev > 10 !== next > 10
)

In the example above, the hook will only change if the state's data.chairs property is below 10 and changes to above 10, or if it is above 10 and changes to below 10. A change from 4 to 11 would cause the state to update; a change from 11 to 12 would not.

---

createSelectorHook

createSelectorHook(state)

This is a helper that will generate a selector hook from a state. The hook returned by createSelectorHook is unlike the useSelector shown above in that you will not have to enter the state as a first argument.

import { createState, createSelectorHook } from '@state-designer/react'

const state = createState({
  data: {
    tables: 0,
    chairs: 0,
  },
  on: {
    ADDED_TABLE: (data) => data.tables++,
    ADDED_CHAIRS: (data) => data.chairs++,
  },
})

const useSelector = createSelectorHook(state)

function TablesCounter() {
  const tables = useSelector((state) => state.data.tables)
  return <button onClick={() => state.send('ADDED_TABLE')}>{tables}</button>
}