了解语言特性最快的方式是调试诡异的代码

Paste_Image.png

补充1

<script>
    var a=[1,2,3];
    var b=a;
    a=[4,5,6];
    console.log(b);
    //[1,2,3]

    var a=[1,2,3];
    var b=a;
    a.pop();
    console.log(b);
    //[1,2]
</script>

补充2 this

<script>
    function sayLocation() {
        console.log(this.atWhere)
    }
    var atWhere = "I am in global";
    sayLocation();
    //I am in global
</script>

<script>
    'use strict';
    function sayLocation() {
        console.log(this.atWhere);
    }
    var atWhere = "I am in global";
    sayLocation();
    // Uncaught TypeError
</script>

<script>
    var name = "global";
    function person() {
        console.log(this.name); 
        //"global"
        person.name = 'inside';
        function sayName() {
            console.log(this.name);
            //"global"
        }
        sayName();
    }
    person();
</script>

<script>
function say() {
    console.log(this.name);
}
var obj1 = {
    name: "1",
    say: say
}
var obj2 = {
    name: "2",
    say: say
}
obj1.say();
//1
obj2.say();
//2
</script>

<script>
    function say() {
        console.log(this.name);
    }
    var name = "global";
    var obj = {
        name: "inside",
        say: say
    }
    obj.say();
    //inside
    var alias = obj.say;
    alias();
    //global
</script>

<script>
    function speak() {
        console.log(this.name);
    }
    var name = "global";
    var obj1 = {
        name: 'obj1'
    }
    var obj2 = {
        name: 'obj2'
    }
    speak();
    //global
    speak.call(window);
    //global
    speak.call(obj1);
    //obj1
    speak.call(obj2);
    //obj2
</script>

<script>
    function count(x,y) {
        console.log(this.a*x+y);
    }
    var obj1 = {
        a: 2
    }
    var obj2 = {
        a: 3
    }
    count.call(obj1, 1, 2) 
    //4
    count.apply(obj1, [1, 2]) 
    //4
    count.call(obj2, 1, 2) 
    //5
    count.apply(obj2, [1, 2]) 
    //5
</script>

<script>
    function count(x,y) {
        console.log(this.a*x+y);
    }
    var obj1 = {
        a:2
    }
    var bound1 = count.bind(obj1);
    bound1(1, 2);
    var bound2 = count.bind(obj1, 1);
    bound2(2);
    var bound3 = count.bind(obj1, 1, 2);
    bound3();
    var bound4 = count.bind(obj1, 1, 2, 3);
    //指定了多余的参数,多余的参数会被忽略
    bound4();
    //4
</script>

<script>
    function Person(name,age) {
        this.name = name;
        this.age = age;
        console.log("f");
    }
    Person("n",0);
    //f
    console.log(name);
    //n
    console.log(age);
    //0
    var n=new Person("n",0);
    //f
    console.log(n.name);
    //n
    console.log(n.age);
    //0
</script>

<script>
    function speak() {
        console.log(this.name);
    }
    var obj1 = {
        name: 'obj1',
        speak: speak
    }
    var obj2 = {
        name: 'obj2'
    }
    obj1.speak();
    //obj1
    obj1.speak.call(obj2);
    //obj2
</script>

<script>
    function foo(something) {
        this.a = something;
    }
    var obj1 = {};
    var bar = foo.bind(obj1);  
    //返回一个新函数bar，这个新函数内的this指向了obj1
    bar(2); 
    console.log(obj1.a);
    //2
    var baz = new bar(3)
    //调用new 操作符后，bar函数的this指向了返回的新实例baz
    console.log(obj1.a);
    //2
    console.log(baz.a);
    //3 
</script>

<script>
    var a = 1;
    var foo = () => {
        console.log(this.a);
    }
    var obj = {
        a: 2
    }
    foo();
    //1
    foo.call(obj);
    //1
</script>

<script>
    function Person(name,age) {
        this.name = name
        this.age = age 
        this.speak = function (){
            console.log(this.name)
            //普通函数
        }
        this.bornYear = () => {
            //箭头函数
            console.log(new Date().getFullYear() - this.age)
        }
    }
    var n = new Person("n",10)
    n.speak() 
    //'n'
    n.bornYear() 
    //2007
    var m = {
        name: "m",
        age: 100
    }
    n.speak.call(m)
    //'m'
    n.bornYear.call(m)
    //2007
</script>
    

补充3：apply

<script>
    function Person(name,age){
        this.name=name; 
        this.age=age;  
        this.sayhello=function(){console.log("hello")};
    }
    function Print(){          
        this.funcName="Print"; 
        this.show=function(){      
            var msg=[];
            for(var key in this){ 
                if(typeof(this[key])!="function"){
                    msg.push([key,":",this[key]].join(""));
                }
            }
            console.log(msg.join(" "));
        };
    }
    function Student(name,age,grade,school){    
        Person.apply(this,arguments);
        Print.apply(this);
        this.grade=grade;                
        this.school=school;           
    } 
    var p1=new Person("jake",10);
    p1.sayhello();
    var s1=new Student("tom",13,6,"清华小学");
    s1.show();
    s1.sayhello();
    console.log(s1.funcName);
    //hello
    //name:tom age:13 funcName:Print grade:6 school:清华小学
    //hello
    //Print
</script>

<script>
    function getMax(arr){
        var arrLen=arr.length;
        for(var i=0,ret=arr[0];i<arrLen;i++){
            ret=Math.max(ret,arr[i]);
        }
        return ret;
    }
    function getMax2(arr){
        return Math.max.apply(null,arr);
    }
    var a=[1,2,3];
    console.log(getMax(a));
    console.log(getMax2(a));
    //3

    var arr1=[1,2,3];
    var arr2=[4,5,6];

    Array.prototype.push.apply(arr1,arr2);
    console.log(arr1);
    //[1,2,3,4,5,6]
</script>

《javascript权威教程》

//p37
//二进制浮点数
var x=.3-.2;
var y=.2-.1;
console.log(x==y);
//false
console.log(x==.1);
//false
console.log(y==.1);
//true

//p38
//日期
var then=new Date(2017,0,8);
//2017 1 14 周日
console.log(then.getMonth());
//0
console.log(then.getDate());
//8
console.log(then.getDay());
//0

//p40
//转义
console.log('you\'re right');

//p43
//object true
if(0!==null){
    console.log('excute');
}
//excute
var o={};
if(o){
    console.log('excute');
}
//excute
var o;
if(o){
    console.log('excute');
}
//no excute

//p57
//全局变量
var global=this;

//p58
//包装对象
var s="s";
s.property='property';
alert(s.property);
//undefind

//显式创建包装对象
var s='string';
var S=new String(s);
console.log(S.length);
S.length=100;
console.log(S.length);
S.wtf="sonof";
console.log(S.wtf);
//6
//6
//sonof

//p59
var s='hello';
s.toUpperCase();
console.log(s.toUpperCase());
//HELLO
console.log(s);
//hello
s=s.toUpperCase();
console.log(s);
//HELLO

//p60
//数组、对象永不相等
var o1={x:1};
var o2={x:1};
console.log(o1==o2);
//false
var arr1=[1,2];
var arr2=[1,2];
console.log(arr1==arr2);
//false

<script>
    //对象值都是引用
    var a=[];
    var b=a;
    b[0]=1;
    console.log(a[0]);
    //1
    console.log(b===a);
    //true
</script>

<script>
    //类型转换
    console.log(10+'object');
    //string '10object'
    console.log('7'*'4');
    //numeric 28
    console.log(n=1-'x');
    //NaN
    console.log(n+'object');
    //string NaNobject
</script>

<script>
    //p62
    //转换和相等性
    console.log(null==undefined);
    console.log('0'==0);
    console.log(0==false);
    console.log('0'==false);
    //all true
</script>

<script>
    //显式转换
    console.log(Number(3));
    //3
    console.log(String(false));
    //'false'
    console.log(Boolean([]));
    //true
    console.log(Object(3));
    //=>new Number(3);
</script>

<script>
    //p67
    var now=new Date();
    console.log(now+1);
    //string
    console.log(now-1);
    //number
    console.log(now==now.toString());
    //true
</script>

<script>
    //p68
    //不使用var，造成的作用域问题
    var scope='global';
    function checkscope(){
        scope='local';
        return scope;
    }
    checkscope();
    console.log(scope);
    //local
</script>

<script>
    //p69
    //函数作用域，非类c{}作用域
    function test(){
        var i=0;
        if(1){
            var j=0;
            for(var k=0;k<10;k++){
                //console.log(k);
            }
            console.log(k);
            //10
        }
        console.log(j);
        //0
    }
    test();
</script>

<script>
    //p70
    //删除全局变量
    var truevar=1;
    //不可删除全局“变量”
    fakevar1=2;
    //全局“对象”的一个可删除属性
    this.fakevar2=3
    //同fakevar1
    console.log(delete truevar);
    //false
    console.log(delete fakevar1);
    //true
    console.log(delete fakevar2);
    //true
</script>

<script>
    //p75
    var square=function(x){return x*x;}
    console.log(square(2));
    //4
</script>

<script>
    //p83
    console.log('1'+2);
    //string '12'
    console.log(1+{});
    //string '1[object Object]'
    console.log(true+true);
    //2
    console.log(2+null);
    //2
    console.log(2+undefined);
    //NaN
</script>

<script>
    //p84
    var i=1,j=++i;
    console.log(i);
    //2
    console.log(j);
    //2
    var i=1,j=i++;
    console.log(i);
    //2
    console.log(j);
    //1
</script>

<script>
    //p87
    //js对象比较是引用比较，不是值比较
    var a=null;
    var b=null;
    console.log(a===b);
    //true勘误
    var a=undefined;
    var b=undefined;
    console.log(a===b);
    //true勘误
    var a=null;
    var b=undefined;
    console.log(a==b);
    var a=NaN;
    var b=NaN;
    console.log(a==b);
    console.log(a===b);
    //false
    console.log(a==a);
    console.log(a===a);
    //false
    a={x:1,y:2};
    b={x:1,y:2};
    console.log(a==b);
    console.log(a===b);
    //false
    var a=null;
    var b=undefined;
    console.log(a==b);
    //true
    console.log('1'==1);
    //true
    console.log(true==1);
    //true
    console.log(false==0);
    //true
</script>

<script>
    //p89
    console.log('11'<'2');
    //true
    console.log('1'<2);
    //true
    console.log('one'<3)
    //false 'one'->NaN<3
</script>

<script>
    //p90
    var p={x:1,y:1};
    console.log('toString' in p);
    //true

    var d=[7,8,9];
    console.log(7 in d);
    //false
    console.log(0 in d);
    //true
    console.log(3 in d);
    //false
</script>

<script>
    //p92
    //短路
    if(a==b) stop();
    (a==b) && stop();
</script>

<script>
    //p95
    var i=0;
    var data=[1,2];
    data[i++]*=2;
    console.log(data);
    console.log(i);
    //[2,2]
    //1

    var i=0;
    var data=[1,2,3];
    data[++i]*=2;
    console.log(data);
    console.log(i);
    //[1,4,3]
    //1

    var i=0;
    var data=[1,2];
    data[i++]=data[i++]*2;
    console.log(data);
    console.log(i);
    //[4,2]
    //2

    var i=0;
    var data=[1,2,3];
    data[++i]=data[++i]*2;
    console.log(data);
    console.log(i);
    //[1,6,3]
    //2
</script>

<script>
    //96
    //eval解释运行有js源代码组成的字符串
    console.log(eval('3+2'));
    //5
    f=function(){
        eval('function f(x){return x+1}');
        return f(1);
    }
    console.log(f());
    //2
</script>

<script>
    //p97
    var x='global';
    function f(){
        var x='local';
        eval("x+=' changed'");
        return x;
    }
    console.log(f(),x);
    //local changed global

    geval=eval;
    var y='global';
    function g(){
        var y='local';
        geval("y+=' changed'");
        return y;
    }
    console.log(g(),y);
    //local global changed
</script>

<script>
    //p100
    var o={x:1,y:2};
    delete o.x;
    console.log(o);
    //{y:2}

    var a=[1,2,3];
    delete a[2];
    console.log(a);
    //[1,2]
    console.log(a.length);
    //3

    var o={x:1,y:2};
    console.log(delete o.x);
    //true
    console.log(typeof o.x);
    //undefined
    console.log(delete o.x);
    //true 删除不存在的属性，返回true
    console.log(delete o);
    //false 不能删除通过var申明的变量
    this.x=1;
    console.log(delete x);
    //true
    console.log(x);
    //运行时错误
</script>

<script>
    //p117
    var o={x:1,y:2,z:3};
    var a=[],i=0;
    for(a[i++] in o);
    console.log(a);
    //['x','y','z']
    for(x in a) console.log(x);
    //0 1 2
</script>

<script>
    //p123
    //阶层函数
    function factorial(x){
        if(x<0) throw new Error('x不能是负数');
        for(var f=1;x>1;f*=x,x--);
        return f;
    }
    try{
        var n=Number(prompt('请输入一个正整数',''));
        var f=factorial(n);
        alert(n+'!='+f);
    }
    catch(ex){
        alert(ex);
    }
    finally{}
</script>

<script>
    //p126
/*
    with(document.forms[0]){
        name.value='';
        address.value='';
        email.value='';
    }
*/

    var o={x:1,y:2};
    with(o) x=10;
    console.log(o);
    //{x:10,y:2}
</script>

<script>
    //p126
    //断点调试
    function f(o){
        if(o===undefined) debugger;
        console.log('functon excute');
    }
    f();
</script>

<script>
    //p134
    //通过原型继承创建一个新对象
    function inherit(p){
        if(p==null) throw TypeError();
        if(Object.create)
            return Object.create(p);
        var t=typeof p;
        if(t!=="object" && t!=="function") throw TypeError();
        function f(){}
        f.prototype=p;
        return new f(); 
    }
    //防止对o的意外修改
    var o={x:'dont\'t change this value};
    library_function(inherit(o));
</script>

<script>
    //137
    //通过原型继承创建一个新对象
    function inherit(p){
        if(p==null) throw TypeError();
        if(Object.create)
            return Object.create(p);
        var t=typeof p;
        if(t!=="object" && t!=="function") throw TypeError();
        function f(){}
        f.prototype=p;
        return new f(); 
    }
    var o={};
    o.x=1;
    var p=inherit(o);
    p.y=2;
    var q=inherit(p);
    q.z=3;
    console.log(q.x);
    console.log(q.y);
    console.log(q.z);
</script>

//138
//通过原型继承创建一个新对象
function inherit(p){
    if(p==null) throw TypeError();
    if(Object.create)
        return Object.create(p);
    var t=typeof p;
    if(t!=="object" && t!=="function") throw TypeError();
    function f(){}
    f.prototype=p;
    return new f(); 
}
var unitcircle={r:1};
var c=inherit(unitcircle);
c.r=2;
console.log(unitcircle.r);
//1

<script>
    //p138
    var book={subtitle:{length:100}}
    var len=undefined;
    if(book){
        if(book.subtitle) len=book.subtitle.length;
    }
    console.log(len);
    //100

    var book={subtitle:{length:100}}
    var len=undefined;
    len=book && book.subtitle && book.subtitle.length;
    console.log(len);
    //100
</script>

<script>
    //p140
    function inherit(p){
        if(p==null) throw TypeError();
        if(Object.create)
            return Object.create(p);
        var t=typeof p;
        if(t!=="object" && t!=="function") throw TypeError();
        function f(){}
        f.prototype=p;
        return new f(); 
    }
    var p={x:1};
    var q=inherit(p);
    p.y=2;
    console.log(p);
    //{x:1,y:2}
    console.log(q);
    //{x:1,y:2}
    console.log(delete q.y);
    //true
    console.log(q);
    //{x:1,y:2}
    q.z=3;
    console.log(p);
    //{x:1,y:2}
</script>

<script>
    //p140
    var x=1;
    console.log(delete this.x);
    //false
    console.log(x);
    //1
    function f(){};
    console.log(delete this.f);
    //false
    this.y=1;
    console.log(delete y);
    //true
    console.log(y);
    //undefined error
</script>

<script>
    var o={x:1,y:1};
    function d(){
        var o={x:2,y:2};
        delete o.x;
        console.log(o);
    }
    d();
    //{y:2}
</script>

<script>
    //p141
    function inherit(p){
        if(p==null) throw TypeError();
        if(Object.create)
            return Object.create(p);
        var t=typeof p;
        if(t!=="object" && t!=="function") throw TypeError();
        function f(){}
        f.prototype=p;
        return new f(); 
    }
    var o=inherit({y:2});
    o.x=1;
    console.log('x' in o);
    //true
    console.log(o.propertyIsEnumerable('x'));
    //true
    console.log(o.hasOwnProperty('x'));
    //true
    console.log('y' in o);
    //true
    console.log(o.propertyIsEnumerable('y'));
    //false
    console.log(o.hasOwnProperty('y'));
    //false
    //继承而来不可枚举
</script>

<script>
    //p142
    for(p in o){
        if(!o.hasOwnProperty(p)) continue;//跳过继承的属性
    }
    for(p in o){
        if(typeof o[p]==='function') continue;//跳过方法
    }
</script>

<script>
    //p142
    function extend(o,p){
        for(prop in p){
            o[prop]=p[prop];
        }
        return o;
    }
    var o={};
    var p={x:1,y:2};
    console.log(extend(o,p));
    //{x:1,y:2}
    p.z=3;
    console.log(o);
    //{x:1,y:2}
    var p={x:1,y:2};
    var o=p;
    console.log(o);
    //{x:1,y:2}
    p.z=3;
    console.log(o);
    //{x:1,y:2,z:3}
</script>

<script>
    //p143
    function merge(o,p){
        for(prop in p){
            if(o.hasOwnProperty[prop]) continue;
            o[prop]=p[prop];    
        }
    }
    function restrict(o,p){
        for(prop in o){
            if(!(prop in p)) delete o[prop];
        }
        return o;
    }
    function union(o,p){return extend(extend({},o),p)}
    //extend{o,p} if coding like this,o changed
    function intersection(o,p){return restrict(extend({},o),p)}
</script>

<script>
    //p144
    function keys(o){
        if(typeof o !=='object') throw TypeError();
        var result=[];
        for(var prop in o){
            if(o.hasOwnProperty(prop))
                result.push(prop);
        }
        return result;
    }
    //keys()类似于Object.keys() Object.getOwnPropertyNames()
</script>

<script>
    //145
    function inherit(p){
        if(p==null) throw TypeError();
        if(Object.create)
            return Object.create(p);
        var t=typeof p;
        if(t!=="object" && t!=="function") throw TypeError();
        function f(){}
        f.prototype=p;
        return new f(); 
    }
    var p={
        x:1.0,
        y:1.0,
        get r(){return Math.sqrt(this.x*this.x+this.y*this.y);},
        set r(newvalue){
            var oldvalue=Math.sqrt(this.x*this.x+this.y*this.y);
            var ratio=newvalue/oldvalue;
            this.x*=ratio;
            this.y*=ratio;
        },
        get theta(){return Math.atan2(this.y,this.x);}
    };
    var q=inherit(p);
    q.x=1,q.y=1;
    console.log(q.r);
    console.log(q.theta);

    var serialnum={
        $n:0,
        get next(){return this.$n++;},
        set next(n){
            if(n>=this.$n){
                this.$n=n;
            }else{
                throw '< illegal';
            }
        }
    }
    snum=inherit(serialnum);
    console.log(snum.next);
    //0
    console.log(snum.next);
    //1
    snum.next=-99;
    //error < illegal
</script>

<script>
    //p147
    var o={};
    Object.defineProperty(o,'x',{
        value:1,
        writable:true,
        enumerable:false,
        configurable:true});
    console.log(o.x);
    //1
    console.log(Object.keys(o));
    //[]不可枚举
    Object.defineProperty(o,'x',{
        writable:false
    });
    console.log(o.x=2);
    //2
    console.log(o.x);
    //1
    Object.defineProperty(o,'x',{
        value:2
    });
    console.log(o.x);
    //2
    //只读，但是可配置configurable
    Object.defineProperty(o,'x',{
        get:function(){return 0}
    });
    console.log(o.x);
    //0
</script>

<script>
    //p148
    var p=Object.defineProperties({},{
        x:{value:1,writable:true,enumerable:true,configurable:true},
        y:{value:1,writable:true,enumerable:true,configurable:true},
        z:{
            get:function(){return Math.sqrt(this.x*this.x+this.y*this.y)},
            enumerable:true,
            configurable:true
        },
    });
</script>

<script>
    //149
    //?
    Object.defineProperty(Object.prototype,
        'extend',
        {
            writable:true,
            enumerable:false,
            configurable:true,
            value:function(o){
                var names=Object.getOwnPropertyNames(o);
                for(var i=0;i<names.length;i++){
                    if(names[i] in this) continue;
                    var desc=Object.getOwnPropertyDescriptor(o,names[i]);
                    Object.defineProperty(this,names[i],desc);
                }
            }
        })
</script>

<script>
    var p={x:1};
    var o=Object.create(p);
    console.log(p.isPrototypeOf(o));
    //true
    console.log(Object.prototype.isPrototypeOf(p));
    //true

    function classof(o){
        if(o===null) return 'Null';
        if(o===undefined) return 'Undefined';
        return Object.prototype.toString.call(0).slice(8,-1);
    }

    //Object.preventExtensions()
    //Object.seal()
    //Object.freeze()
</script>

<script>
    //p151  
    var p={x:1};
    var o=Object.create(p);
    console.log(p.isPrototypeOf(o));
    //true
    console.log(Object.prototype.isPrototypeOf(p));
    //true

    function classof(o){
        if(o===null) return 'Null';
        if(o===undefined) return 'Undefined';
        return Object.prototype.toString.call(0).slice(8,-1);
    }

    //Object.preventExtensions()
    //Object.seal()
    //Object.freeze()

    o={x:1,y:{z:[false,null,'']}};
    s=JSON.stringify(o);
    p=JSON.parse(s);
</script>

<script>
    //168
    var data=[1,2,3,4,5];
    data.forEach(function(v,i,a){a[i]=v+1;});
    console.log(data);
    
    //170
    var a=[1,2,3,4,5];
    var sum=a.reduce(function(x,y){return x+y},0);
    console.log(sum);
    //15
    var product=a.reduce(function(x,y){return x*y},1);
    console.log(product);
    //120
    var max=a.reduce(function(x,y){return x>y?x:y});
    console.log(max);
    //5

    //p171
    var a=[2,3,4];
    var fn=function(accumulator,value){
        return Math.pow(value,accumulator);
    };
    console.log(a.reduceRight(fn));
    console.log(a.reduce(fn));
</script>

<script>
    //p172
    function extend(o,p){
        for(prop in p){
            o[prop]=p[prop];
        }
        return o;
    }
    function union(o,p){return extend(extend({},o),p)}
    var objects=[{x:1},{y:2},{z:3}];
    var merged=objects.reduce(union);
    console.log(merged);
    //{x:1;y:2;z:3}

    var objects=[{x:1,a:1},{y:2,a:2},{z:3,a:3}];
    console.log(objects.reduce(union));
    //{x:1,y:2,z:3,a:3}
    console.log(objects.reduceRight(union));
    //{x:1,y:2,z:3,a:1}
</script>

<script>
    //172
    a=[1,1,2,1,0,1];
    console.log(a.indexOf(1));
    //0
    console.log(a.indexOf(1,1));
    //1
    console.log(a.lastIndexOf(1));
    //5
    console.log(a.indexOf(3));
    //-1

    function findall(a,x){
        var results=[],
            len=a.length,
            pos=0;
        while(pos<len){
            pos=a.indexOf(x,pos);
            if(pos===-1) break;
            results.push(pos);
            pos=pos+1;
        }
        return results;
    }
    console.log(findall(a,1));
    //[0,1,3,5]
</script>

<script>
    //175
    var a={'0':'a','1':'b','2':'c',length:3};
    console.log(Array.prototype.join.call(a,"+"));
    //'a+b+c'
    console.log(Array.prototype.slice.call(a,0));
    //['a','b','c']
    console.log(Array.prototype.map.call(a,function(x){
        return x.toUpperCase();
    }));
    //['A','B','C']

    var s='test';
    console.log(s.charAt(0));
    //t
    console.log(s[1]);
    //e

    s='Javascript';
    console.log(Array.prototype.join.call(s,' '));
    //J a v a s c r i p t
    console.log(Array.prototype.filter.call(s,
        function(x){
            return x.match(/[^aeiou]/);
        }).join(''));
    //Jvscrpt
</script>

<script>
    //p178
    function factorial(x){
        if(x<=1) return 1;
        return x*factorial(x-1);
    }

    var calculator={
        operand1:1,
        operand2:1,
        add:function(){
            this.result=this.operand1+this.operand2;
        }
    };
    calculator.add();
    console.log(calculator.result);
    //2
</script>

<script>
    //p183
    var o={
        m:function(){
            var self=this;
            console.log(this===o);
            f();

            function f(){
                console.log(this===o);
                console.log(self===o);
            }
        }
    };
    o.m();
    //true
    //false
    //true
</script>

<script>
    //p185
    function getPropertyNames(o,a){
        if(a===undefined) a=[];
        //a=a || [];
        for(var property in o) a.push(property);
        return a;
    }

    function f(x,y,z){
        if(arguments.length!=3){
            throw new Error('function f called with'+arguments.length+'arguments,but it expects 3 arguments');
        }else{
            console.log('execute');
        }
    }
    f(1,2,3);
    f(1,2);
</script>

<script>
    //p186
    console.log(Number.NEGATIVE_INFINITY);
    //-INFINITY
    function max(){
        var max=Number.NEGATIVE_INFINITY;
        for(var i=0;i<arguments.length;i++){
            if(arguments[i]>max){max=arguments[i]}
        }
        return max;
    }
    console.log(max(1,2,3,4,5,6,7));
    //p187
    function f(x){
        console.log(x);
        arguments[0]=null;
        console.log(x);
    }
    f(1);
    //p188
    var factorial=function(x){
        if(x<=1) return 1;
        return x* arguments.callee(x-1);
        //callee
    }
    console.log(factorial(3));
    //p188
    function arraycopy(from,from_start,to,to_start,length){
        for(f in from){
            if(f>=from_start && f<from_start+length){
                to[to_start+(f-from_start)]=from[f];
            }
        }
        return to;
    }
    function easycopy(args){
        return arraycopy(args.from,
                        args.from_start || 0,
                        args.to,
                        args.to_start || 0,
                        args.length);
    }
    console.log(easycopy({from:[1,2,3,4,5,6,7],from_start:2,to:[],to_start:4,length:2}));
</script>