deepstate

A ClojureScript microlib for state management in a Helix based / React app

The problem

React hooks and re-frame are from different worlds and don't play nicely together.

deepstate provides some simple hooks-based state management primitives which maybe aren't very efficient in a large app, but are simple, flexible and straightforward in an async world.

Usage

(require '[deepstate.action :as a]')

The model and state

There is a single state value (per action-context). The state should be pure data.

Actions get dispatched in response to events in the app and are then handled, and the result of handling an action is some effects, which are functions which are used to update the state.

Actions

Actions are maps which describe an operation to mutate state. They have an ::a/action key which selects a handler, and whatever other keys the handler requires.

dispatch

An action is dispatched causing a handler to be invoked according to the ::a/action key in the action. The handler returns some Effects which can be:

• (fn [state] ...) - an ::a/update-now function to update state
• Promise<Effects> - an ::a/update-later promise of Effects
• a map:

    {::a/update-now (fn [state] ...)
     ::a/navigate (fn [state] ...)
     ::a/update-later Promise<Effects>}

any ::a/update-now fn will be immediately used to update state, and any ::a/navigate fn will be used to navigate. ::a/update-later will be recursively waited on and processed until all effects have been completed.

def-action

Defines an action handler. It takes

• the ::a/action key used in an action map
• a parameter destructuring vector for the single action map parameter
• the body defining the effects the handler returns - which may use the bindings destructured from the action map

(a/def-action ::change-query
  [{q :q
    :as _action}]
  (fn [state]
    (assoc state ::query q)))

def-async-action

Defines a promise-based async action handler. The action is specified as a form returning a promise of the result. The state of the action will be managed and reported on with a standard data schema, with the result (or error) being added to the structure when the action completes.

(a.async/def-async-action ::run-query
   [{q :q
     :as action_}]
  {::a/async (run-query action)
   ::a/navigate-success (fn [{{{id :id} ::a/result} ::a/state}] (str "/item/" id))})

This def-async-action will result in a map in the state at path [::run-query] with the shape

{::a/status ::a/inflight|::a/success|::a/error
 ::a/result ...
 ::a/error ...}

action-context

A React Context which must be provided to use the hooks

use-action

A hook to return the action-context value, which must be provided to dispatch

use-action-state

A hook to access the state. Takes an optional path into the state, without which it returns the entire state

(let [;; all the state
      all-state (a/use-action-state action-context)
      
      ;; just the ::change-query path
      qr (a/use-action-state action-context [::change-query])])

license

Copyright © 2023 mccraigmccraig of the clan mccraig

Distributed under the MIT License.