整理一些最近经常遇到的前端面试题

alert(typeof(null));//object
alert(typeof(NaN));//number
alert(typeof(undefined));//undefined
alert(typeof(“undefined”));//string
alert(NaN == undefined);//false
alert(NaN == NaN);//false

JS:document.getElementById(“div1”).innerHTML;
document.querySelector(“#div1”).innerText;
JQ:$(“#div1”).html()

function addEvent(obj,event,fn){
 //现代：addEventLister 不用加on
 //ie：touchEvent 需要加on
 if (window.addEventListener){
 obj.addEventListener(event,fn);
 }else{
 obj.attachEvent("on"+event, fn);
 }
}

function offset(obj){
 var l = 0;
 var t = 0;
 while(obj){
 l+=obj.offsetLeft;
 t+=obj.offsetTop;
 obj = obj.offsetParent;
 }
 return {left:l,top:t};
}

var util = require('util');
var EventEmitter = require('events');
function MyEmitter() {
 EventEmitter.call(this);
} // 构造函数
util.inherits(MyEmitter, EventEmitter); // 继承
var em = new MyEmitter();
em.on('hello', function(data) {
 console.log('收到事件hello的数据:', data);
}); // 接收事件，并打印到控制台
em.emit('hello', 'EventEmitter传递消息真方便!');

var fs = require("fs");
var rs = fs.createReadStream(“1.jpg");
var ws = fs.createWriteStream("2.jpg");
rs.pipe(ws);

var http = require("http");
var queryString = require("querystring");
var server = http.createServer(function (req,res) {
 if(urlObj.pathname == "/post"){
 var str = "";
 req.on("data",function (chunk) {
 str+=chunk;
 });
 req.on("end",function () {
 var query = queryString.parse(str);
 console.log(query);
 })
 res.end("你请求的地址是"+urlObj.pathname);
 }
});
server.listen(8080);

var http = require("http");
var request = http.request({
 host:"localhost",
 port:"8080",
 path:"/request",
 method:"post"
},function (res) {
 res.on("data",function (chunk) {
 console.log(chunk.toString());
 });
});
request.write("user=zhang&pass=111");
request.end("请求结束");//结束本次请求

//obj.imgArr 图片数组
//obj.loadingProgress 加载进度
//obj.loadingOver 加载结果
(function (){
 var imgObjs = [];
 loadingFn = function (obj) {
 var index = 0; 
 for (var i = 0; i < obj.imgArr.length; i++) {
 var imgObj = new Image();
 imgObj.onload = function() {
 index++;
 imgObjs.push(this);
 if (obj.loadingProgress){
 obj.loadingProgress(index, this);
 }
 if (index > obj.imgArr.length-1){
 obj.loadingOver(imgObjs);
 }
 }
 imgObj.src = obj.imgArr[i];
 }
 console.log(obj);
 }