1. 递归

sayHi();    function sayHi(){    alert("Hi!");}sayHi(); //错误：函数还不存在    var sayHi = function(){    alert("Hi!");};//不要这样做！ if(condition){    function sayHi(){        alert("Hi!");    }} else {    function sayHi(){        alert("Yo!");    }}//可以这样做var sayHi;if(condition){    sayHi = function(){        alert("Hi!");    };} else {    sayHi = function(){        alert("Yo!");    };}function factorial(num){     if (num <= 1){         return 1;     } else {         return num * factorial(num-1);     }}var anotherFactorial = factorial;factorial = null;alert(anotherFactorial(4)); //出错！function factorial(num){    if (num <= 1){        return 1;    } else {        return num * arguments.callee(num-1);    }}var factorial = (function f(num){    if (num <= 1){        return 1;    } else {        return num * f(num-1);    }});

• 函数声明提升；

2. 闭包

2.1 闭包与变量

2.2 关于 this 对象

2.3 内存泄漏

3. 模仿块级作用域

(function(){    //这里是块级作用域})();function outputNumbers(count){    (function () {        for (var i=0; i < count; i++){            alert(i);        }    })();    alert(i); //导致一个错误！}(function(){    var now = new Date();    if (now.getMonth() == 0 && now.getDate() == 1){        alert("Happy new year!");    }})();

• 这种做法可以减少闭包占用的内存问题，因为没有指向匿名函数的引用。
  只要函数执行完毕，就可以立即销毁其作用域链了。

4. 私有变量

//特权方法function Person(name){    this.getName = function(){        return name;    };    this.setName = function (value) {        name = value;    };}var person = new Person("Nicholas");alert(person.getName()); //"Nicholas"person.setName("Greg");alert(person.getName()); //"Greg"

4.1 静态私有变量

(function(){    var name = "";    Person = function(value){        name = value;    };    Person.prototype.getName = function(){        return name;    };    Person.prototype.setName = function (value){        name = value;    };})();var person1 = new Person("Nicholas");alert(person1.getName()); //"Nicholas"person1.setName("Greg");alert(person1.getName()); //"Greg"var person2 = new Person("Michael");alert(person1.getName()); //"Michael"alert(person2.getName()); //"Michael"

4.2 模块模式

var application = function(){    //私有变量和函数    var components = new Array();    //初始化    components.push(new BaseComponent());    //公共    return {            getComponentCount : function(){            return components.length;        },        registerComponent : function(component){            if (typeof component == "object"){                components.push(component);            }        }    };}();

4.3 增强的模块模式

var application = function(){    //私有变量和函数    var components = new Array();    //初始化    components.push(new BaseComponent());    //创建 application 的一个局部副本    var app = new BaseComponent();    //公共接口    app.getComponentCount = function(){        return components.length;    };    app.registerComponent = function(component){        if (typeof component == "object"){            components.push(component);        }    };    //返回这个副本    return app;}();