Slice and compose redux-type reducers.

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README.md

redux-sac

Slice redux objects (reducers, middleware, ...)

subReducer(key, reducer, additionalKey, ...)

Creates a wrapper reducer that calls reducer on the sub-state specified by key. Key can go in different formats, see deepGetOrNil below. Rest of the state is left untouched.

const r = subReducer("persons", personReducer);
  
r({persons: ["John", "Jill"], cars: ["Honda"]}, action);
// => {
//   persons: personReducer(["John", "Jill"], action), 
//   cars: ["Honda"]
// }

Respects redux convention that if no change was made, the identical object should be returned. So in previous case, if personReducer would return the identical array, r would return the state object it was passed in.

If persons were deeper in hierarchy, it could have been created as const r = subReducer("files.persons", personReducer); for example.

You may pass additional keys as addition arguments. In that case, additional parts of state will be fetched and passed to a sub-reducer:

const r = subReducer("persons", personReducer, "assets.cars");
  
r({persons: ["John", "Jill"], assets: {cars: ["Honda"]}}, action);
// => {
//   persons: personReducer(["John", "Jill"], action, ["Honda"]), 
//   assets: {cars: ["Honda"]}
// }

This technique is mentioned in Redux docs, in "Beyond combineReducers" page.

subMiddleware(key | selectorFn, middleware)

Creates a wrapper middleware on the sub-state specified by key or the selector function selectorFn by decorating getState part of the passed arg. The key can have different format, see deepGetOrNil below. Rest of the passed arg is left untouched.

const r = subMiddleware("persons", ({getState}) => next => action => {
  console.log(JSON.stringify(getState()));
  return next(action);
});
  
const altR = subMiddleware(state => state.persons, ({getState}) => next => action => {
  console.log(JSON.stringify(getState()));
  return next(action);
});
  
// use r or altR in creation of store
  
store.getState();
// => {persons: ["John", "Jill"], cars: ["Honda"]}
store.dispatch({type: "any"});
// console => ["John","Jill"] 

If persons were deeper in hierarchy, it could have been created as const r = subMiddleware("files.persons", ...); for example.

You can use subMiddleware to sub-state anything getting one parameter in which one of the properties passed is getState function; it is not special-case for middleware. For example, it is usable for wrapping redux-effex effect function.

subEffex(key | selectorFn, effects)

Creates a wrapper around each element of the effects array on the sub-state specified by key or by selector function selectorFn by decorating effect function with subMiddleware and returns the array of the wrapped effects.

const effects = [{
  action: "foo",
  effect: ({getState}) => {
    console.log(JSON.stringify(getState()));
  }
}];
  
const e = subEffex("persons", effects);
const altE = subEffex(state => state.persons, effects);
  
// use e or altE in creation of store
  
store.getState();
// => {persons: ["John", "Jill"], cars: ["Honda"]}
store.dispatch({type: "foo"});
// console => ["John","Jill"] 

Compose

composeReducers(reducer1, reducer2, ...)

Creates a wrapper reducer that calls passed reducers one after another, passing intermediate states. and returning the result of the last one.

Useful to "concatenate" a few subReducers. like:

composeReducers(
  subReducer("files.persons", personReducer, "assets.swag"),
  subReducer("files.clients", clientReducer, "news"),
  subReducer("assets", assetReducer),
  baseReducer
)

Redux helpers

typedAction(type, [fn])

This creates an action creator function that amends existing fn by:

  • adding a type property to the result, as well as
  • adding a TYPE property to action creator itself.

So for example:

export const answerQuestion =
  typedAction("answer question", (index, answer) => ({
    payload: {index, answer}
  }));

allows you to call answerQuestion(2, "Albert Einstein") to create {type: "answer question", payload: {index: 2, answer: "Albert Einstein"}}; but it also allows you to use case answerQuestion.TYPE: in your reducer, since answerQuestion.TYPE === "answer question". IOW, this removes the two-space problem of having const FOO_BAR_TYPE as well as fooBar action creator.

In case you don't pass the fn argument, the action creator only creates {type}.