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function isArray(value){ return Object.prototype.toString.call(value) == "[object Array]"; }
也可以基于这一思路测试某个值是不是原生函数或正则表达式：
//判断是否原生函数 function isFunction(value){ return Object.prototype.toString.call(value) == "[object Function]"; } //判断是否原生函数 function isFunction(value){ return Object.prototype.toString.call(value) == "[object RegExp]"; }
function Person(name,age,job){ if(this instanceof Person){ //判断this是否是正确的类型 this.name = name; this.age = age; this.job = job; }else{ return new Person(name,age,job); } } var per1 = Person("Nicholas",29,"Software Engineer"); alert(window.name); //"" alert(per1.name); //"Nicholas" var per2 = new Person("Shelby",34,"Ergonomist"); alert(per2.name); //"Shelby"
function createXHR(){ if(typeof XMLHttpRequest != "undefined"){ return new XMLHttpRequest; }else if(typeof ActiveXObject != "undefined"){ if(typeof arguments.callee.activeXString != "string"){ var versions = ["MSXML2.XMLHttp.6.0","MSXML2.XMLHttp.3.0","MSXML2.XMLHttp"],i,len; for(i=0,len=versions.length;i < len;i++){ try{ new ActiveXObject(versions[i]); arguments.callee.activeXString = versions[i]; break; }catch(ex){ //跳过 } } } return new ActiveXObject(arguments.callee.activeXString); }else{ throw new Error("No XHR Object available"); } }
function createXHR(){ if(typeof XMLHttpRequest != "undefined"){ createXHR = function(){ //将原函数覆盖 return new XMLHttpRequest(); }; }else if(typeof ActiveXObject != "undefined"){ createXHR = function(){ //将原函数覆盖 if(typeof arguments.callee.activeXString != "string"){ var versions = ["MSXML2.XMLHttp.6.0","MSXML2.XMLHttp.3.0","MSXML2.XMLHttp"],i,len; for(i=0,len=versions.length;i < len;i++){ try{ new ActiveXObject(versions[i]); arguments.callee.activeXString = versions[i]; break; }catch(ex){ //跳过 } } } return new ActiveXObject(arguments.callee.activeXString); }; }else{ createXHR = function(){ //将原函数覆盖 throw new Error("No XHR object available."); }; } return createXHR(); }
方法2、在声明函数时指定适当的函数，这样第一次调用函数不损失性能，在代码首次加载时会损失性能
var createXHR = (function(){ if(typeof XMLHttpRequest != "undefined"){ return function(){ return new XMLHttpRequest(); }; }else if(typeof ActiveXObject != "undefined"){ return function(){ if(typeof arguments.callee.activeXString != "string"){ var versions = ["MSXML2.XMLHttp.6.0","MSXML2.XMLHttp.3.0","MSXML2.XMLHttp"],i,len; for(i=0,len=versions.length;i < len;i++){ try{ new ActiveXObject(versions[i]); arguments.callee.activeXString = versions[i]; break; }catch(ex){ //跳过 } } } return new ActiveXObject(arguments.callee.activeXString); }; }else{ return function(){ throw new Error("No XHR object available."); }; } })();
var handler = { message : "Event handled", handleClick : function(event){ alert(this.message); } }; var btn = document.getElementById("my-btn"); EventUtil.addHandler(btn,"click",handler.handleClick); //按钮按下显示undefined，不显示Event handled
按下按钮实际显示的是undefined，并不会显示Event handled。问题在于没有保存handler.handleClick的环境，所以this最后指向了DOM按钮，而非handler（IE8中this指向window），可以使用闭包解决问题：
var handler = { message : "Event handled", handleClick : function(event){ alert(this.message); } }; var btn = document.getElementById("my-btn"); EventUtil.addHandler(btn,"click",function(event){ handler.handleClick(event); //按钮按下显示Event handled });
//bind函数解决方案 function bind(fn,context){ return function(){ return fn.apply(context,arguments); }; }
调用方法：
EventUtil.addHandler(btn,"click",bind(handler.handleClick,handler)); ECMAScript5为所有函数定义了原生的bind函数，进一步简化了操作。调用方法 EventUtil.addHandler(btn,"click",handler.handleClick.bind(handler)); //传入作为this的对象
支持的浏览器：IE9+，Firefox4+，Chrome
var person = { name : "name"}; Object.preventExtensions(person); person.age = 28; alert(person.age); //undefined Object.isExtensible可检测对象是否可扩展
var person = { name : "name" }; alert(Object.isExtensible(person)); //true alert(Object.isSealed(person)); //false Object.seal(person); alert(Object.isExtensible(person)); //false alert(Object.isSealed(person)); //true
var found /*Boolean*/ = false;
//CSS对于JavaScript的紧密耦合 element.style.color = "red"; element.style.backgroundColor = "blue"; //CSS对于JavaScript的松散耦合 elements.className = "edit";
var Constants = { INVALID_VALUE_MSG:"Invalid value!", INVALID_VALUE_URL:"/errors/invalid.php" }; function validate(value){ if(!value){ alert(Constants.INVALID_VALUE_MSG); location.href = Constants.INVALID_VALUE_URL; } }
//4个语句---浪费 var count = 5; var color = "red"; var values = [1,2,3]; var now = new Date(); //一个语句 var count = 5; color = "red"; values = [1,2,3]; now = new Date();
var name = values[i]; i++; //合并 var name = values[i++];
JavaScript高级程序设计（第三版）学习笔记22、24、25章
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原文地址：http://www.cnblogs.com/TwinklingZ/p/5280970.html
