JavaScript中数组reduce()方法使用详情_javascript技巧_

arr.reduce(function(tmp, value, [index]) { // dosomething... }, [startValue]) // 提供初始值通常更安全

let arr = [1, 2, 3, 4] let sum = arr.reduce((x,y) => x + y) // 求和 let mul = arr.reduce((x,y) => x * y) // 求乘积 let average = arr.reduce((x, y) => (x + y) / arr.length) // 求平均值

const list = [ { name:'张三', age:20 }, { name:'李四', age:15 }, { name:'王五', age:35} ] const newList = list.filter(item => item.age > 18).map(item => { return Object.assign({}, item, { is: '成年' }) })

const newList = list.reduce((tmp, item) => { return item.age > 18 ? tmp.concat(Object.assign({}, item, { is: '成年' })) : tmp }, []) console.log(newList)

let person = [ {id: 0, name: "小明"}, {id: 1, name: "小张"}, {id: 2, name: "小李"}, {id: 3, name: "小孙"}, {id: 1, name: "小周"}, {id: 2, name: "小陈"}, ] let obj = {} person = person.reduce((prev,item)=>{ if(obj[item.id] === undefined) { prev.push(item) obj[item.id] = 1 } return prev }, []) console.log(person)

const result = [ {subject: '物理', marks: 41}, {subject: '化学', marks: 59}, {subject: '高等数学', marks: 36}, {subject: '应用数学', marks: 90}, {subject: '英语', marks: 64}, ] let initialValue = { pass: [], fail: [] } const groupedResult = result.reduce((accumulator, current) => { (current.marks >= 50) ? accumulator.pass.push(current) : accumulator.fail.push(current) return accumulator }, initialValue) console.log(groupedResult)