@f/reduce-key

reduce-key

Reduce a keyed map (or array), using a selector function.

Installation

$ npm install @f/reduce-key

Usage

One thing that often prevents the fully declarative construction of reducers is keyed maps (e.g. objects of the form {[key]: entity}, or arrays). reduceKey solves this problem, by allowing you to specify a selector function that decides which subject to apply the reducer to.

var reduceKey = require('@f/reduce-key')

const todoReducer = combineReducers({
  text: handleActions({
    [TODO_SET_TEXT]: (state, {text}) => text,
    [TODO_CLEAR_TEXT]: () => ''
  }),
  completed: handleActions({
    [TOGGLE_COMPLETED]: (state) => !state
  })
})

export default combineReducers({
  todos: reduceKey((state, {idx}) => idx, todoReducer)
})

API

reduceKey(select, reduce)

• select - A function that accepts state and action and returns the key. If select returns null, undefined, or false, the reducer will not be called. So you are free to do things like: (state, action) => action.payload.key - even if your actions do not always contain key.
• reduce - A reducer that reduces over the entities within the map or array.

Returns: A reducer that reduces over the sub-object in the key and returns a new copy of the map, with the sub-object specified by select(state, action) updated by your reducer.

License

MIT