feat(ch10): implement a redux reducer

src/ch-10_abstraction-and-composition/10.1_abstraction-and-composition.test.js

@@ -1,5 +1,15 @@
 import {expect} from 'chai';
-import {add, addN, compose, composeRight, filterRed, map, mapRedu, pipe} from "./10.1_abstraction_and_composition";
+import {
+    add,
+    ADD_VALUE, addingReducer,
+    addN,
+    compose,
+    composeRight,
+    filterRed,
+    map,
+    mapRedu,
+    pipe
+} from "./10.1_abstraction_and_composition";
 
 describe("Abstraction and Composition", () => {
     it("should fix a parameter in a function", () => {
@@ -76,6 +86,16 @@ describe("Abstraction and Composition", () => {
         const pipedFn = pipe(add1, add5, multiplyWith3);
 
         expect(pipedFn(5)).to.equal(33);
+    });
+
+    it("should implement a redux reducer", () => {
+        const actions = [
+            {type: ADD_VALUE, payload: {value: 1}},
+            {type: ADD_VALUE, payload: {value: 1}},
+            {type: ADD_VALUE, payload: {value: 1}},
+        ];
+
+        expect(actions.reduce(addingReducer, 0)).to.equal(3);
     })
 
 });

src/ch-10_abstraction-and-composition/10.1_abstraction_and_composition.js

@@ -17,3 +17,15 @@ export const compose = (...fns) => x => fns.reduceRight((y, f) => f(y), x);
 export const composeRight = (...fns) => x => fns.reverse().reduce((y, f) => f(y), x);
 
 export const pipe = (...fns) => x => fns.reduce((y, f) => f(y), x);
+
+export const ADD_VALUE = 'ADD_VALUE';
+export const addingReducer = (state = 0, action = {}) => {
+    const {type, payload} = action;
+
+    switch (type) {
+        case ADD_VALUE:
+            return state + payload.value;
+        default:
+            return state;
+    }
+};

src/ch-10_abstraction-and-composition/README.md

@@ -28,3 +28,15 @@ Good abstractions are:
 ## Reduce 
 - Fold
 - Accumulate
+
+## Redux reducer
+- Library/architecture
+- To manage app state
+- Takes current state -> add action object -> returns new state
+
+### Rules
+- Reducer with no params returns initial state
+- Reducer not handling action type returns state
+- Reducers must be pure functions
+
+