Higher-order-reducers NPM

higher-order-reducers

A simple utility belt library for building and composing redux reducers using higher order functions.

installation

From command line, call yarn add higher-order-reducers or npm install --save higher-order-reducers

motivation

This project has sprung from the work I've done with redux and more and more complex reducers, where I've noticed a lot of boilerplate simple repeating itself. Despite the clean and simple philosophies of redux, I often ran into code like

const someReducer = (state = DEFAULT_STATE, action) {
  switch(action.type) {
    case TYPE1:
    case TYPE2:
      // Some specific logic here
    case TYPE3:
      // other logic
    default:
      return state;
  }
}

Sometimes with so many case calls that eslint would complain about the complexity of the "simple" reducer.

So, inspired by how recompose uses higher-level-components to elegantly compose react components, I started experimenting with trying to extract some functional patterns from the above code. The result is the groundwork of this library. In the specific case above, it would be rewritten as

import { compose, withDefault, cloneState, mapByType } from "higher-order-reducers";
const someReducer = compose([
    withDefault(DEFAULT_STATE)),
    cloneState,
    mapByType({
      TYPE1: () => {},
      TYPE2: () => {},
      TYPE3: () => {}
    })
]);

Is that better? I'm not sure. I think it's prettier, but it might be slower. Regardless I felt that this was a fun project to share with the world, if anybody cares. I will probably continue to code like this until somebody proves to me that it's objectively worse than the alternative.

functions

`withDefault(defaultState)`

Returns a reducer that returns the supplied defaultState if the state it's supplied is undefined

import { withDefault } from "higher-order-reducers";
const reducer = withDefault(2);
reducer(); //2
reducer(1); //1

`cloneState`

Returns a deep clone of the supplied state. It is literally just an alias for JSON.parse(JSON.stringify(state)), which is by far the fastest way to perform that operation. However, it only works with plain objects (and arrays of them), and does not work with object instances, functions, regexes et cetera. If something like that is required, consider either implementing your own clone function that is built to clone your specific state as quickly as possible, or use something like lodash.cloneDeep, but be aware of the performance implications

`mapByType(reducerMap)`

Return a reducer that maps action types to specific reducer functions, and returns the result (or the original state if the map does not contain the key)

import { mapByType } from "higher-order-reducers";
const reducer = mapByType({
  'ACTION_ONE': (state, action) => action.value,
  'ACTION_TWO': () => 2
});
reducer('', {type: 'ACTION_ONE', value: 'hello'}); //'hello'
reducer('', {type: 'ACTION_TWO'}); //2
reducer('state', {type: 'ACTION_THREE'}) //'state'

`mergeStates(reducer)`

Merges the keys returned by the reducer into the current state instead of replacing it entirely

import { mergeStates } from "higher-order-reducers";
const animal = (state, action) => {noise: action.noise, feet: action.feet};
const reducer = mergeStates(animal);
reducer({name: "duck", noise: "quack"}, {noise: "moo", feet: 4}); //{name: "duck", noise: "moo", feet: 4}

`compose(reducers)`

Creates a reducer that generates the state by calling the supplied reducers in order, with the output of the previous reducer as the input for the next, without changing the action.

import { compose } from "higher-order-reducers";
const add = (state, action) => state + action.value;
const reducer = compose([
  add,
  add,
  add
]);
reducer(1, {value: 2}) //7

`chain(reducers)`

Creates a reducer that starts calling the first reducer in the array with supplied state and action, but an additional next parameter, that, when called, will call the next reducer in order with the supplied state and the original action. If next is not called by a reducer, the chain will stop.

import { chain } from "higher-order-reducers";
const addAndContinue = (state, action, next) => next(state + action.value);
const stop = (state) => state;
const reducer = chain([
  addAndContinue,
  addAndContinue,
  stop, //next is not called here, chain will stop
  addAndContinue
]);
reducer(1, {value: 2}) //5

`link(reducer)`

Meant to be used with chain, simply converts the reducer to chainable by always calling next with its result.

import { chain, link } from "higher-order-reducers";
const add = (state, action) => state + action.value;
const reducer = chain([
  link(add),
  link(add),
  link(add)
]);
reducer(1, {value: 2}) //7

`linkIf(predicate)`

Meant to be used with chain. Creates a reducer that will only call next if the supplied predicate (called with state and action) returns truthy. Otherwise stops the chain with the value it was supplied.

import { chain, linkIf } from "higher-order-reducers";
const add = (state, action) => state + action.value;
const onlyIfEven = linkIf(state, action) => (action.value % 2 === 0);

const reducer = chain([
  onlyIfEven,
  add
]);

reducer(1, {value: 1}) //1
reducer(1, {value: 2}) //3

`linkIfType(allowedTypes)`

Meant to by used with chain. A special case of the filter method that only proceeds if the action type field matches a value in the supplied array.

import { chain, linkIfType } from "higher-order-reducers";
const add = (state, action) => state + action.value;
const onlyIfAdd = linkIfType(["ADD_VALUE"])

const reducer = chain([
  onlyIfAdd,
  add
]);

reducer(1, {value: 1, type: "SUBTRACT_VALUE"}) //1
reducer(1, {value: 2, type: "ADD_VALUE"}) //3

`linkedChain(reducers)`

A special version of chain that automatically links reducers together if they don't explicitly accept the third next parameter.

import { linkedChain } from "higher-order-reducers";
const add = (state, action) => state + action.value;
const addAndContinue = (state, action, next) => next(state + action.value);
const stop = (state, action, next) => state;

const reducer = linkedChain([
  add, //next is not explicitly accepted here, so linkedChain will continue
  addAndContinue, //here next is called, so linkedChain will continue
  stop, //this function accepts next, but doesn't call it, so the chain stops
  add
]);
reducer(1, {value: 2}) //5