阿里前端常见面试题（附答案）

document.addEventListener("click", function(e) {    if (e.target.nodeName == "A")        console.log("a");}, false);

document.addEventListener("click", function(e) {    var node = e.target;    while (node.parentNode.nodeName != "BODY") {        if (node.nodeName == "A") {            console.log("a");            break;        }        node = node.parentNode;    }}, false);

function search(arr, target, start, end) {  let targetIndex = -1;
  let mid = Math.floor((start + end) / 2);
  if (arr[mid] === target) {    targetIndex = mid;    return targetIndex;  }
  if (start >= end) {    return targetIndex;  }
  if (arr[mid] < target) {    return search(arr, target, mid + 1, end);  } else {    return search(arr, target, start, mid - 1);  }}// const dataArr = [1, 2, 3, 4, 5, 6, 7, 8, 9];// const position = search(dataArr, 6, 0, dataArr.length - 1);// if (position !== -1) {//   console.log(`目标元素在数组中的位置:${position}`);// } else {//   console.log("目标元素不在数组中");// }

div{    border: 100px solid transparent;    width: 0;    heigt: 0;    border-radius: 100px;    border-top-color: red;}

git branch 查看本地所有分支git status 查看当前状态 git commit 提交 git branch -a 查看所有的分支git branch -r 查看远程所有分支git commit -am "nit" 提交并且加注释 git remote add origin git@192.168.1.119:ndshowgit push origin master 将文件给推到服务器上 git remote show origin 显示远程库origin里的资源 git push origin master:developgit push origin master:hb-dev 将本地库与服务器上的库进行关联 git checkout --track origin/dev 切换到远程dev分支git branch -D master develop 删除本地库developgit checkout -b dev 建立一个新的本地分支devgit merge origin/dev 将分支dev与当前分支进行合并git checkout dev 切换到本地dev分支git remote show 查看远程库git add .git rm 文件名(包括路径) 从git中删除指定文件git clone git://github.com/schacon/grit.git 从服务器上将代码给拉下来git config --list 看所有用户git ls-files 看已经被提交的git rm [file name] 删除一个文件git commit -a 提交当前repos的所有的改变git add [file name] 添加一个文件到git indexgit commit -v 当你用－v参数的时候可以看commit的差异git commit -m "This is the message describing the commit" 添加commit信息git commit -a -a是代表add，把所有的change加到git index里然后再commitgit commit -a -v 一般提交命令git log 看你commit的日志git diff 查看尚未暂存的更新git rm a.a 移除文件(从暂存区和工作区中删除)git rm --cached a.a 移除文件(只从暂存区中删除)git commit -m "remove" 移除文件(从Git中删除)git rm -f a.a 强行移除修改后文件(从暂存区和工作区中删除)git diff --cached 或 $ git diff --staged 查看尚未提交的更新git stash push 将文件给push到一个临时空间中git stash pop 将文件从临时空间pop下来

function Foo(){    Foo.a = function(){        console.log(1);    }    this.a = function(){        console.log(2)    }}
Foo.prototype.a = function(){    console.log(3);}
Foo.a = function(){    console.log(4);}
Foo.a();let obj = new Foo();obj.a();Foo.a();

async function async1 () {  console.log('async1 start');  await new Promise(resolve => {    console.log('promise1')  })  console.log('async1 success');  return 'async1 end'}console.log('srcipt start')async1().then(res => console.log(res))console.log('srcipt end')

script startasync1 startpromise1script end

首先说明什么是闭包，闭包简单来说就是函数嵌套函数，内部函数引用来外部函数的变量，从而导致垃圾回收机制没有把当前变量回收掉，这样的操作带来了内存泄漏的影响，当内存泄漏到一定程度会影响你的项目运行变得卡顿等等问题。因此在项目中我们要尽量避免内存泄漏。

var myObject = {    foo: "bar",    func: function() {        var self = this;        console.log(this.foo);          console.log(self.foo);          (function() {            console.log(this.foo);              console.log(self.foo);          }());    }};myObject.func();

Promise.resolve().then(() => {    console.log('1');    throw 'Error';}).then(() => {    console.log('2');}).catch(() => {    console.log('3');    throw 'Error';}).then(() => {    console.log('4');}).catch(() => {    console.log('5');}).then(() => {    console.log('6');});

1 3 5 6

const obj = { a: {        b: 1,        c: 2,        d: {e: 5}    }, b: [1, 3, {a: 2, b: 3}], c: 3}
flatten(obj) 结果返回如下// {//  'a.b': 1,//  'a.c': 2,//  'a.d.e': 5,//  'b[0]': 1,//  'b[1]': 3,//  'b[2].a': 2,//  'b[2].b': 3//   c: 3// }

function isObject(val) {  return typeof val === "object" && val !== null;}
function flatten(obj) {  if (!isObject(obj)) {    return;  }  let res = {};  const dfs = (cur, prefix) => {    if (isObject(cur)) {      if (Array.isArray(cur)) {        cur.forEach((item, index) => {          dfs(item, `${prefix}[${index}]`);        });      } else {        for (let k in cur) {          dfs(cur[k], `${prefix}${prefix ? "." : ""}${k}`);        }      }    } else {      res[prefix] = cur;    }  };  dfs(obj, "");
  return res;}flatten();

Promise.allSettled = function(promises) {    return new Promise((resolve, reject) => {        if(Array.isArray(promises)) {            if(promises.length === 0) return resolve(promises);            let result = [];            let count = 0;            promises.forEach((item, index) => {                Promise.resolve(item).then(                    value => {                        count++;                        result[index] = {                            status: 'fulfilled',                            value: value                        };                        if(count === promises.length) resolve(result);                    },                     reason => {                        count++;                        result[index] = {                            status: 'rejected'.                            reason: reason                        };                        if(count === promises.length) resolve(result);                    }                );            });        }        else return reject(new TypeError("Argument is not iterable"));    });}

'hello tuture' instanceof String // false

a = 1;var a;console.log(a);

var tmp = new Date();
function fn(){    console.log(tmp);    if(false){        var tmp = 'hello world';    }}
fn();  // undefined

var tmp = 'hello world';
for (var i = 0; i < tmp.length; i++) {    console.log(tmp[i]);}
console.log(i); // 11