以下是个人在工作中收藏总结的一些关于javascript数组方法reduce的相关代码片段，后续遇到其他使用这个函数的场景，将会陆续添加，这里作为备忘。
javascript数组那么多方法，为什么我要单挑reduce方法，一个原因是我对这个方法掌握不够，不能够用到随心所欲。另一个方面，我也感觉到了这个方法的庞大魅力，在许多的场景中发挥着神奇的作用。
理解reduce函数
reduce() 方法接收一个函数作为累加器（accumulator），数组中的每个值（从左到右）开始缩减，最终为一个值。
arr.reduce([callback, initialValue])
看如下例子：
let arr = [1, 2, 3, 4, 5];
// 10代表初始值，p代表每一次的累加值，在第一次为10
// 如果不存在初始值，那么p第一次值为1
// 此时累加的结果为15
let sum = arr.reduce((p, c) => p + c, 10); // 25
// 转成es5的写法即为：
var sum = arr.reduce(function(p, c) {
console.log(p);
return p + c;
}, 10);
片段一：字母游戏
const anagrams = str => {
if (str.length <= 2) {
return str.length === 2 "").reduce((acc, letter, i) => {
return acc.concat(anagrams(str.slice(0, i) + str.slice(i + 1)).map(val => letter + val));
}, []);
}
anagrams("abc"); // 结果会是什么呢？
reduce负责筛选出每一次执行的首字母，递归负责对剩下字母的排列组合。
片段二：累加器
const sum = arr => arr.reduce((acc, val) => acc + val, 0); sum([1, 2, 3]);
片段三：计数器
const countOccurrences = (arr, value) => arr.reduce((a, v) => v === value "color: #ff0000">片段四：函数柯里化函数柯里化的目的就是为了储存数据，然后在最后一步执行。
const curry = (fn, arity = fn.length, ...args) => arity <= args.length "color: #ff0000">片段五：数组扁平化const deepFlatten = arr => arr.reduce((a, v) => a.concat(Array.isArray(v) "color: #ff0000">片段六：生成菲波列契数组const fibonacci = n => Array(n).fill(0).reduce((acc, val, i) => acc.concat(i > 1 "color: #ff0000">片段七：管道加工器const pipe = (...funcs) => arg => funcs.reduce((acc, func) => func(acc), arg); pipe(btoa, x => x.toUpperCase())("Test");通过对传递的参数进行函数加工，之后将加工之后的数据作为下一个函数的参数，这样层层传递下去。
片段八：中间件
const dispatch = action => { console.log('action', action); return action; } const middleware1 = dispatch => { return action => { console.log("middleware1"); const result = dispatch(action); console.log("after middleware1"); return result; } } const middleware2 = dispatch => { return action => { console.log("middleware2"); const result = dispatch(action); console.log("after middleware2"); return result; } } const middleware3 = dispatch => { return action => { console.log("middleware3"); const result = dispatch(action); console.log("after middleware3"); return result; } } const compose = middlewares => middlewares.reduce((a, b) => args => a(b(args))) const middlewares = [middleware1, middleware2, middleware3]; const afterDispatch = compose(middlewares)(dispatch); const testAction = arg => { return { type: "TEST_ACTION", params: arg }; }; afterDispatch(testAction("1111"));
redux中经典的compose函数中运用了这种方式，通过对中间件的重重层叠，在真正发起action的时候触发函数执行。 片段九：redux-actions对state的加工片段// redux-actions/src/handleAction.js const handleAction = (type, reducer, defaultState) => { const types = type.toString(); const [nextReducer, throwReducer] = [reducer, reducer]; return (state = defaultState, action) => { const { type: actionType } = action; if (!actionType || types.indexOf(actionType.toString()) === -1) { return state; } return (action.error === true "sourceCode">片段十：数据加工器片段十一：对象空值判断const reducers = { totalInEuros: (state, item) => { return state.euros += item.price * 0.897424392; }, totalInYen: (state, item) => { return state.yens += item.price * 113.852; } }; const manageReducers = reducers => { return (state, item) => { return Object.keys(reducers).reduce((nextState, key) => { reducers[key](state, item); return state; }, {}) } } const bigTotalPriceReducer = manageReducers(reducers); const initialState = { euros: 0, yens: 0 }; const items = [{ price: 10 }, { price: 120 }, { price: 1000 }]; const totals = items.reduce(bigTotalPriceReducer, initialState);let school = { name: 'Hope middle school', created: '2001', classes: [ { name: '三年二班', teachers: [ { name: '张二蛋', age: 26, sex: '男', actor: '班主任' }, { name: '王小妞', age: 23, sex: '女', actor: '英语老师' } ] }, { name: '明星班', teachers: [ { name: '欧阳娜娜', age: 29, sex: '女', actor: '班主任' }, { name: '李易峰', age: 28, sex: '男', actor: '体育老师' }, { name: '杨幂', age: 111, sex: '女', actor: '艺术老师' } ] } ] }; // 常规做法 school.classes && school.classes[0] && school.classes[0].teachers && school.classes[0].teachers[0] && school.classes[0].teachers[0].name // reduce方法 const get = (p, o) => p.reduce((xs, x) => (xs && xs[x] "sourceCode">片段十二：分组const groupBy = (arr, func) => arr.map(typeof func === 'function' "sourceCode">首先通过map计算出所有的键值，然后再根据建值进行归类 片段十三：对象过滤const pick = (obj, arr) =>
arr.reduce((acc, curr) => (curr in obj && (acc[curr] = obj[curr]), acc), {});pick({ a: 1, b: '2', c: 3 }, ['a', 'c']);
根据给出的键值来遍历，比较对象中是否存在相同键值的的值，然后通过逗号表达式把赋值后的对象赋给下一个的初始值
片段十四：数组中删除指定位置的值
const remove = (arr, func) => Array.isArray(arr) "codepen" data-pen-title="reduce pick" data-embed-version="2" data-user="rynxiao" data-default-tab="js" data-slug-hash="QaqONY" data-theme-id="0" data-height="265">首先根据
filter函数过滤出数组中符合条件的值，然后使用reduce在原数组中删除符合条件的值，可以得出最后arr的值变成了[1, 3]片段十五：promise按照顺序执行
const runPromisesInSeries = ps => ps.reduce((p, next) => p.then(next), Promise.resolve()); const delay = d => new Promise(r => setTimeout(r, d)); const print = args => new Promise(r => r(args)); runPromisesInSeries([() => delay(1000), () => delay(2000), () => print('hello')]);片段十六：排序
const orderBy = (arr, props, orders) => [...arr].sort((a, b) => props.reduce((acc, prop, i) => { if (acc === 0) { const [p1, p2] = orders && orders[i] === 'desc' "codepen" data-pen-title="reduce runPromisesInSeries" data-embed-version="2" data-user="rynxiao" data-default-tab="js" data-slug-hash="QaqOMR" data-theme-id="0" data-height="265">片段十七：选择const select = (from, selector) => selector.split('.').reduce((prev, cur) => prev && prev[cur], from); const obj = { selector: { to: { val: 'val to select' } } }; select(obj, 'selector.to.val');以上就是我们为大家整理的关于js数组方法reduce经典用法代码内容，感谢你对的支持。