这边列举了5个前端经典的面试题

首先我们来看一下题目，都各自思考一下，自己是否能够做出来。然后再跟后面的答案对比一下

题目1

var a = {n:1}var b = {n:2}b.x = a = {n:3}console.log(b.x)a.x = a = {n:3}console.log(a.x)

题目2

（1）var start = new Date()setTimeout(function() {    console.log(new Date() -start)}, 500)（2）var start = new Date()setTimeout(function() {    console.log(new Date() -start)}, 500)while((new Date() - start <= 1000) {}

题目3

var log = console.logvar hint = window.alertvar write = document.writelog('123')hint('123')wirte('123')

题目4

var name = 'A'function getName() {    return this.name}var obj = {    name: 'B',    getName: function() {        return this.name    },    showName:function(a) {        console.log(getName())        console.log(a())        console.log(a === arguments[0])        console.log(arguments[0]())    } }obj .showName(getName, 1)

题目5

async function async1() {    console.log('async1 start')    await async2()    console.log('async1 end')}async function async2() {    console.log(async2())}console.log('script start')setTimeout(function() {    console.log('setTimeout')}, 0)async1()new Promise(function (resolve) {    console.log('promise1')    resolve()}).then(function() {    console.log('promise2')})console.log('script end')

答案1

console.log(b.x)   // {n:3}console.log(a.x)   // undefined这是跟js的优先级有关的 .的优先级最高，因此先计算左边的b.x,a.x

答案2

(1)console.log(new Date() -start)  // 不是一定500,而是大于等于500主要是由于定时器的时间不一定准，这个跟异步的机制有关当定时器的时间到了之后，执行函数会进入栈中，会根据栈中的执行任务，依次执行（不懂的可以学习一下异步机制）(2)console.log(new Date() -start)  // 大于等于1000由于是单线程

答案3

log('123') // 正常hint('123') // 正常write('123') // 报错这是由于write是相当于window.write；而document.write下面应该会用到this对象，所以会报错应当改成window.write(document, '123')

答案4

console.log(getName()) // 'A'  this === windowconsole.log(a()) // 'A' this === windowconsole.log(a === arguments[0]) // trueconsole.log(arguments[0]()) // undefined this 为argument对象

答案5

script startasync1 startasync2promise1async1 endscript endpromise2setTimeout这一块跟异步有关先同步，后异步，在回调。还有promise机制