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今日问题:

  1. 实例化一个函数的时候,new关键字的过程是怎样的?

  2. 什么是js阻塞?

  3. 下面代码的执行结果是什么?

for(var i = 0 ; i < 10; i++){ setTimeout(function(){  console.log(i); }, 0);}

昨日解答:

  1. 如何检测数据是否是数组类型?

答:ES5定义了Array.isArray()方法,但是仅支持IE9+,兼容性不好;instanceof方法可以判断变量是否是数组类型,但是只限同一全局环境之内,在一个页面有多个iframe的情况下,instanceof失效;最好的办法是使用Object.prototype.toString.call(value)。

  1. alert([1,2,3])的结果是什么?

答:alert只能接受字符串参数,因此内部会对参数自动调用toString方法,所以结果为“1,2,3”。

  1. arguments.callee.caller是什么意思?

答:arguments.callee返回使用该参数的函数对象,caller返回调用该函数对象的函数。

  1. jQuery中get和eq的区别是什么?

答:get返回原生dom对象,eq返回jquery对象

  1. setTimeout("alert(1)",0);alert(2);返回值是什么?

答:2,1。setTimeout会将函数加入 异步队列,等待同步队列中的函数执行完毕再去执行。

  1. 什么是原型和构造器?

答:我们创建的每个函数都有一个prototype属性,这个属性是一个指针,指向一个对象,而这个对象的用途是包含可以由特定类型的所有实例共享的属性和方法;默认情况下所有原型对象都会自动获得一个constructor属性,这个属性包含一个指向prototype属性所在函数的指针。如:Person.prototype.constructor指向Person。

  1. 专门写一篇博客探讨

  2. 借用浏览器的定时线程,典型案例是setTimeout

  3. 参照以下代码:

/** * vlstat 浏览器统计脚本 */var statIdName = "vlstatId";var /** * 设置cookieId */function setCookie(c_name, value, expiredays) {  var exdate = new Date();  exdate.setDate(exdate.getDate() + expiredays);  document.cookie = c_name + "=" + escape(value) + ((expiredays == null) ? "" : ";expires=" + exdate.toGMTString()) + ";path=/;domain=cecb2b.com";}/** * 获取cookieId */function getCookie(c_name) {  if (document.cookie.length > 0) {    c_start = document.cookie.indexOf(c_name + "=");    if (c_start != -1) {      c_start = c_start + c_name.length + 1;      c_end = document.cookie.indexOf(";", c_start);      if (c_end == -1) {        c_end = document.cookie.length;      }      return unescape(document.cookie.substring(c_start, c_end));    }  }  return "";}/** * 获取当前时间戳 */function getTimestamp() {  var timestamp = Date.parse(new Date());  return timestamp;}/** * 生成statId */function genStatId() {  var cookieId = getTimestamp();  cookieId = "vlstat" + "-" + cookieId + "-" + Math.round(Math.random() * 3000000000);  return cookieId;}/** * 设置StatId */function setStatId() {  var cookieId = genStatId();  setCookie(statIdName, cookieId, 365);}/** * 获取StatId */function getStatId() {  var statId = getCookie(statIdName);  if (statId != null && statId.length > 0) {    return statId;  } else {    setStatId();    return getStatId();  }}/** * 获取UA */function getUA() {  var ua = navigator.userAgent;  if (ua.length > 250) {    ua = ua.substring(0, 250);  }  return ua;}/** * 获取浏览器类型 */function getBrower() {  var ua = getUA();  if (ua.indexOf("Maxthon") != -1) {    return "Maxthon";  } else if (ua.indexOf("MSIE") != -1) {    return "MSIE";  } else if (ua.indexOf("Firefox") != -1) {    return "Firefox";  } else if (ua.indexOf("Chrome") != -1) {    return "Chrome";  } else if (ua.indexOf("Opera") != -1) {    return "Opera";  } else if (ua.indexOf("Safari") != -1) {    return "Safari";  } else {    return "ot";  }}/** * 获取浏览器语言 */function getBrowerLanguage() {  var lang = navigator.browserLanguage;  return lang != null && lang.length > 0 ? lang : "";}/** * 获取操作系统 */function getPlatform() {  return navigator.platform;}/** * 获取页面title */function getPageTitle() {  return document.title;}/** * 创建一个form * * @return */function createSubmitForm() {  var frm = document.createElement("form");  document.body.appendChild(frm);  frm.method = "POST";  return frm;}/** * 为form创建一个元素 * * @param inputForm * @param elementName * @param elementValue * @return */function createFormElement(frmInput, elementName, elementValue) {  var element = document.createElement("input");  element.setAttribute("id", elementName);  element.setAttribute("name", elementName);  element.setAttribute("type", "hidden");  element.setAttribute("value", elementValue);  frmInput.appendChild(element);  return element;}/** * 构造function create() {  if (window.ActiveXObject) {  new ActiveXObject('Microsoft.);  } else if (window.new /** * url指定跳转页,data是要post的数据。func类似于函数指针 * * @param url * @param data * @param func * @return */function AjaxPost(url, data, func) {  var httpRequest = createHttpRequest();  if (httpRequest) {    httpRequest.open("POST", url, true);    httpRequest.setRequestHeader("content-length", data.length);    httpRequest.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");    httpRequest.send(data);    httpRequest.onreadystatechange = function() {      if (httpRequest.readyState == 4) {        try {          if (httpRequest.status == 200) {            if (func) {              // 这里可以调用想要的函数              func(httpRequest.responseText);            }          }        } catch (e) {          alert("Error );        }      }    }  } else {    alert("Error initializing );  }}function vlstatInitLE(vlch, vlch1, vlch2, vlch3) {  var p;  var vlstatCH = vlch != null && vlch.length > 0 ? vlch : "";  var vlstatCH1 = vlch1 != null && vlch1.length > 0 ? vlch1 : "";  var vlstatCH2 = vlch2 != null && vlch2.length > 0 ? vlch2 : "";  var vlstatCH3 = vlch3 != null && vlch3.length > 0 ? vlch3 : "";  var vlstatCookieId = getStatId();  var vlstatUA = encodeURIComponent(getUA());  var vlstatIPAddress = document.localName;  var vlstatREFURL = encodeURIComponent(document.referrer);  var vlstatURL = encodeURIComponent(document.URL);  var vlstatScreenX = screen.width;  var vlstatScreenY = screen.height;  var vlstatOS = getPlatform();  var vlstatBrower = getBrower();  var vlstatBrowerLanguage = getBrowerLanguage();  var vlstatPageTitle = encodeURIComponent(getPageTitle());  var vlstatAction = "index.php";  p = "cookieId=" + vlstatCookieId + "&ua=" + vlstatUA + "&ip=" + vlstatIPAddress + "&refurl="      + vlstatREFURL + "&url=" + vlstatURL + "&screenX=" + vlstatScreenX + "&screenY=" + vlstatScreenY      + "&os=" + vlstatOS + "&brower=" + vlstatBrower + "&browerLang=" + vlstatBrowerLanguage      + "&title=" + vlstatPageTitle + "&ch=" + vlstatCH + "&ch1=" + vlstatCH1 + "&ch2=" + vlstatCH2      + "&ch3=" + vlstatCH3;  var urlGo = vlstatAction + "?" + p;  create'GET', urlGo); null);}
  1. 如何用js判断动画结束?

答:参考以下代码:

/* 探测浏览器种类 */function whichTransitionEvent(){  var t;  var el = document.createElement('fakeelement');  var transitions = {   'transition':'transitionend',   'OTransition':'oTransitionEnd',   'MozTransition':'transitionend',   'WebkitTransition':'webkitTransitionEnd'  }  for(t in transitions){    if( el.style[t] !== undefined ){      return transitions[t];    }  }}/* 监听变换事件! */var transitionEvent = whichTransitionEvent();transitionEvent && e.addEventListener(transitionEvent, function() {  console.log('Transition complete! This is the callback, no library needed!');});