function isArray(value){return Object.prototype.toString.call(value) == "[object Array]";
}

//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"

惰性载入函数

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

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);};
}

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

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

冻结对象

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++];