前端经典手写笔试题

一 请手写拖拽实现

    // 前提条件 元素需要绝对定位，设置left和top属性
    (function () {
        let oDrag = document.getElementById('drag')
        oDrag.onmousedown = (e) => {
            let disx = e.clientX - oDrag.offsetLeft
            let disy = e.clientY - oDrag.offsetTop
            document.onmousemove = (e) => {
                oDrag.style.left = e.clientX - disx + 'px'
                oDrag.style.top = e.clientY - disy + 'px'
            }
            document.onmouseup = () => {
                document.onmousemove = null
                document.onmousedown = null
            }
        }
    })();

二 请手写es6和es5的面向对象代码实现

    // 面向对象
    (function () {
        // es6的面向对象
        class Person {
            constructor(name, age) {
                this.name = name
                this.age = age
            }
            showName() {
                console.log(this.name)
            }
        }
        // 实例化Person
        let student = new Person('王宏', '36')
        student.showName()
        // 继承
        class Worker extends Person {
            constructor(name, age) {
                super(name, age)
            }
            // 添加Worder自己特有的方法
            showAge() {
                console.log(this.age)
            }
        }
        // 实例化Worker
        let coder = new Worker('廖峰', '40')
        coder.showName()
        coder.showAge()

        // es5的面向对象
        function Animal(name, color) {
            this.name = name
            this.color = color
        }
        Animal.prototype.showName = function () {
            console.log(this.name)
        }
        // 实例化Animal对象
        let dragon = new Animal('龙', '金色')
        dragon.showName()

        // 继承
        function Tiger(name, color) {
            Animal.call(this, name, color)
        }
        Tiger.prototype = new Animal()
        Tiger.prototype.constructor = Tiger

        let smallTiger = new Tiger('小老虎', '灰色')

        smallTiger.showName()
    })();

三 请手写tab选项卡

    // tab选项卡
    (function () {
        let oBtnBox = document.getElementsByClassName('btn-box')[0]
        let oContentBox = document.getElementsByClassName('content-box')[0]
        let aBtnItem = oBtnBox.getElementsByTagName('button')
        let aContentBox = oContentBox.getElementsByTagName('div')
        let len = aBtnItem.length
        // 其实用let，那么不需要自定义索引，只用i即可
        for (let i = 0; i < len; i++) {
            aBtnItem[i].idx = i
            aBtnItem[i].onclick = function () {
                for (let j = 0; j < len; j++) {
                    aBtnItem[j].className = ''
                    aContentBox[j].className = 'hide'
                }
                aBtnItem[this['idx']].className = 'active'
                aContentBox[this['idx']].className = ''
            }
        }
    })();

四 请手写ajax的getf方法实现

    // 手写ajax get
    function get(url, fn) {
        let url = 'api/getlist'
        let xhr = XMLHttpRequest()
        xhr.open('GET', url, true)
        xhr.onreadystatechange = function () {
            if (xhr.readyState === 4 && xhr.status === 200) {
                fn(xhr.responseText)
            }
        }
        xhr.send()
    }

五 请手写ajax的post方法实现

    // 手写ajax post
    function post(url, data, fn) {
        let url = 'api/getlist'
        let xhr = XMLHttpRequst()
        xhr.open('POST', url, true)
        xhr.setRequestHeader('Content-Type', 'application/json')
        xhr.onreadystatechange = function () {
            if (xhr.readyState === 4 && xhr.status === 200) {
                fn(xhr.responseText)
            }
        }
        xhr.send(data)
    }

六 请手写jsonp的实现

    // 手写jsonp
    function jsonp(url = '', fn) {
        let fnName = Math.random().toString().slice(2)
        window[fnName] = function (data) {
            fn(data)
        }
        let script = document.creatElement('script')
        script.src = '/api/getlist?cb=' + fnName
        document.body.appendChild(script)
    }

七 请实现递归阶乘函数

    // 手写递归 阶乘
    function jc(n) {
        if (n === 1) {
            return 1
        }
        return n * jc(n - 1)
    }

八 请实现深拷贝对象的函数实现（不考虑函数的拷贝）

    // 深拷贝对象
    function clone(obj) {
        var newObj = obj instanceof 'Array' ? [] : {} // 这种方法obj不能写实体对象，不能直接写{a:12}
        // var newObj = Object.protoType.toString.call(obj).slice(8,-1)
        if (typeof obj === 'object' && typeof obj !== 'null') {
            for (let key in obj) {
                if (typeof obj[key] === 'object' && typeof obj[key] !== 'null') {
                    newObj[key] = clone[obj[key]]
                } else {
                    newObj[key] = obj[key]
                }
            }
        } else {
            return obj
        }
        return newObj
    }