面试手册.md

// 基于发布订阅模式写一个事件事件发布订阅

class Event {
    constructor() {
        this.taskList = {}
    }

    on(eventType, fn) {
        // 触发时， 明白同一个事件可能有多个任务的可能
        // 所以对于task的处理我们都用数组的格式来处理
        let fns = ( this.taskList[eventType] = this.taskList[eventType] || [] )
        if(!fns.include(fn) {
            fns.push(fn)
        }
    }

    emiter(eventType, data) {
        let fns = this.taskList[eventType]
        if(Array.isArray(fns)) {
            fns.map(item => {
                item(data)
            })
        }
        return this
    }

    off(eventType, fn) {
        let fns = this.taskList[type]
        if(Array.isArray(fns)) {
            if(fn) {
                let index = fns.indexOf(callback)
                if(index !== -1) {
                    fns.split(index, 1)
                }
            }else {
                fns.length = 0
            }
        }
        return this
    }
}

实现一手深拷贝

const isType = (value) => {
    return Object.prototype.toString.call(value).match(/(?<= )\w+/)[0]
    // String Number Null Undefined Object Date RegExp Symbol Boolean Function Array
}
const deepClone = obj => {
    let objType = isType(obj)
    let result = {}
    for(let i in obj) {
        if(objType === 'Object' || objType === 'Array') {
            result[i] = deepClone(obj[i])
        }
        result[i] = obj[i]
    }
    return result
}
a = {
    a: 1,
    b: {
        a: 1
    }
}
b = deepClone(a)

千分位

function exchange(num) {
    num = String(num)
    if(num <= 3) {
        return num
    }

    num = num.replace(/\d{1,3}(?=(\d{3})+$)/g, (v) => {
        return v + ','
    })
    return num
}

exchange(1230597)

模拟new关键字

function likeNew (fn, ...args) {
    let o = Object.create(fn.prototype)
    const result = fn.apply(o, args)
    return result || o
}

function Person(name) {
    this.name = name
}
likeNew(Person, 'weihaidong')

// 闭包setTimeout

// 1 setTimeout 外闭包
for(var i = 0; i < 4; i++) {
    ((i) => {
    setTimeout(() => {
        console.log(i)
    }, 1000 * i)
    })(i)
}
// 2 setTimeout 内闭包
for(var i = 0; i < 4; i++) {
    setTimeout(((i) => {
        return () => {
            console.log(i)
        }
    })(i), 1000 * i)
}

isType函数

const isType = v => {
    const reg = /(\.+\s+)/
    return Object.prototype.toString.call(v).replace(/(\[\w+\s+)(\w+)(\])/, '$2')
}
isType(1)

古典继承

function Person(name) {
    this.name = name
}
Person.prototype.getName = function() {
    return this.name
}

function Women(name, sex) {
    // 链接Person属性
    Person.call(this, name)
    // 初始化自身属性
    this.sex = sex
}

// 链接原型链
Women.prototype = Person.prototype
// 修复constructor指向
Women.prototype.constructor = Women

快排

const quickSort = arr => {
    if(arr.length <= 1) return arr
    let [min, flag, max] = arr.reduce((sum, cur, index) => {
        if(index === 0) {
            sum[1].push(cur)
        } else {
            if(cur >= sum[1]) sum[2].push(cur)
            if(cur < sum[1]) sum[0].push(cur)
        }
        return sum
    }, [[], [], []])
    console.log(min, flag, max)
    min = quickSort(min)
    max = quickSort(max)
    return [...min, ...flag, ...max]
}

quickSort([2, 1, 3, 5, 6, 1, 6, 7, 8])

二分法查找

const binarySearch = (arr, x) => {
    console.log(arr)
    if(arr.length <= 1) {
        return arr[0] === x ? x : false
    }
    const flag = Math.floor(arr.length / 2)
    let result
    if(x === arr[flag]) return result = x
    if(x > flag) result = binarySearch(arr.slice(flag), x)
    if(x < flag) result = binarySearch(arr.slice(0, flag), x)
    return result
}
binarySearch([1, 2, 3, 4, 5, 6], 6)
binarySearch([1, 2, 3, 4, 5, 6], 7)

发布订阅

class Event {
    constructor() {
        this.cache = {}
    }

    addEvent(type, fn) {
        if(this.cache[type]) {
            this.cache[type].push(fn)
        } else {
            this.cache[type] = [fn]
        }
    }

    emmitEvent(type, params) {
        const taskList = this.cache[type]
        if(taskList) {
            taskList.map(item => {
                item(params)
            })
        }
    }

    deleteEvent(type) {
        this.cache[type] = []
    }
}

const event = new Event()
event.addEvent('fly', (value) => {
    console.log('i will fly', value)
})
setTimeout(() => {
    event.emmitEvent('fly', 'go')
}, 2000)