day01_手写ES6高阶函数(forEach、map、filter、every、some)

高阶函数

什么是高阶函数?

• 可以把函数作为参数传递给另一个函数

• 可以把函数作为另一个函数的返回结果

forEach

function forEach(list, fn) {
    for (let i = 0; i < list.length; i++) {
        fn(list[i])
    }
}
let arr = [1, 2, 3, 4, 5, 6]
forEach(arr, item => { console.log(item) })

filter

function filter(list, fn) {
    const r = []
    for (let i = 0; i < list.length; i++) {
        if (fn(list[i])) r.push(list[i])
    }
    return r
}

let arr = [1, 2, 3, 4, 5, 6]
const result = filter(arr, item => { return item % 2 == 0 })
console.log(result)

map

function map(list, fn) {
    const r = []
    for (let i = 0; i < list.length; i++) {
        r.push(fn(list[i]))
    }
    return r
}
let arr = [1, 2, 3, 4, 5, 6]
const result = map(arr, item => { return item * 2 })
console.log(result)

some

function some(list, fn) {
    for (let i = 0; i < list.length; i++) {
        if (fn(list[i])) return true
    }
    return false
}
let arr = [1, 2, 3, 4, 5, 6]
const result = some(arr, item => { return item === 3 })
console.log(result)

every

function every(list, fn) {
    for (let i = 0; i < list.length; i++) {
        if (!fn(list[i])) return false
    }
    return true
}
let arr = [1, 1, 1, 1, 1, 2]
const result = every(arr, item => { return item === 1 })
console.log(result)