Built-in, Native, Host object

    Number; // function Number() { [native code] }
    Number = {};
    Number; // Object {}
    var q = 1;
    q; // 1
    typeof q; // "number"
    q.constructor === (1).constructor; // true
    Number = (1).constructor;
    Number; // function Number() { [native code] }

    Number.prototype.multi = function(m) { return this * m; };
    Number = {};
    var q = 5;
    q.constructor.adding = function (a) { return this + a; }
    Number = (1).constructor;
    q.multi(5); // 25
    var w = 6;
    w.multi(5); // 30
    w.adding(4); //10
    Number; // function Number() { [native code] }

    var obj = function () { this.a = 1; this.b = 'a'; };
    var o = new obj;
    obj = null;
    o.constructor; // function () { this.a = 1; this.b = 'a'; };
    var p = new o.constructor;
    p.constructor === o.constructor; // true

    var x = [1, 2, 3];
    typeof x; //"object"
    x instanceof Array; // true
    x instanceof Object; // true

    var x = null;
    var y;
    typeof x; // "object"
    typeof y; // "undefined"
    x instanceof Object; // false

    Number.MIN_VALUE == 5E-324

    Number.MIN_VALUE = 0;

    Number.MIN_VALUE; // 5E-324

    /* native object, Number È®ÀÎ */
    Number; // Number() ==> function Number() { [native code] }
    
    /* a ¸¦ native Number ¸¦ ÀνºÅϽº */
    var a = new Number(55);
    a; // 55 { }
    typeof a; // "object"
    a instanceof Number; // true
    a instanceof Object; // true
    
    /* b ¸¦ ÀνºÅϽº ¾øÀÌ ¼±¾ð */
    var b = 55;
    b; // 55
    typeof b; // "number"
    b instanceof Number; // false
    b instanceof Object; // false
    
    /* a¿Í b¸¦ ºñ±³ */
    a == b; // true
    a.constructor === b.constructor; // true
    
    /* aÀÇ ÇÁ·ÎÆÛƼ È®Àå ¹× È®ÀÎ */
    a[0] = 'This is a number object';
    a[1] = 'Instance of Number';
    a; // 55 { 0: 'This is a number Object', 1: 'Instance of Number' }
    
    a == b // true
    
    /* native object, Number ÀÇ ÇÁ·ÎÅäŸÀÔ ¼³Á¤ */
    Number.prototype.multi = function(m) { return m * this; };
    
    /* a, b È®ÀÎ ¹× È®ÀåµÈ ¸Þ¼Òµå ½ÇÇà¿©ºÎ È®ÀÎ */
    a; // 55 { 0: 'This is a number Object', 1: 'Instance of Number', multi: function() }
    b; // 55
    a.multi(5); // 275
    b.multi(5); // 275
    
    /* native object, Number ÀÇ ÇÁ·ÎÅäŸÀÔ ¼³Á¤ */
    Number.prototype.push = Array.prototype.push;
    
    /* a È®ÀÎ */
    a.length = 2;
    a.push('This is pushed text');
    a; // 55 { 0: 'This is a number Object',
            1: "Instance of Number",
            2: :"This is pushed text",
            length: 3,
            multi: function() ,
            push: function() }
    /* b È®ÀÎ */
    b.push('This is b!');
    b; // 55
    typeof b[0] == "undefined"; // true

    /* º¯¼ö ¼³Á¤ */
    var a1 = new String('asdf');
    var q1 = new Number(5);
    var a2 = 'asdf';
    var q2 = 5;
    var a3 = String('asdf');
    var q3 = Number(5);
    
    /* ¹®ÀÚ¿­ º¯¼ö »ý¼ºÀÚ ¹× ÀνºÅϽº È®ÀÎ */
    a1.constructor === a2.constructor; // true
    a1.constructor === a3.constructor; // true
    a1 instanceof String; // true
    a2 instanceof String; // false
    a3 instanceof String; // false
    
    /* ¼ýÀÚ º¯¼ö »ý¼ºÀÚ ¹× ÀνºÅϽº È®ÀÎ */
    q1.constructor === q2.constructor; // true
    q1.constructor === q3.constructor; // true
    q1 instanceof Number; // true
    q2 instanceof Number; // false
    q3 instanceof Number; // false
    
    /* ¹®ÀÚ¿­ º¯¼ö ÇÁ·ÎÆÛƼ(¶Ç´Â ¸Þ¼Òµå) È®Àå */
    a1.push = a2.push =a3.push = Array.prototype.push;
    a1.push; // function push() { [native code] }
    a2.push; // undefined;
    a3.push; // undefined;
    
    /* ¹®ÀÚ¿­ º¯¼ö length ÇÁ·ÎÆÛƼ °ª ´Ù·ç±â */
    a1.length; // 4
    a2.length; // 4
    a3.lengthl; // 4
    a1.length = 0;
    a1.length; // 4
    a2.length = 0;
    a2.length; // 4
    a3.length = 0;
    a3.length; // 4
    
    /* È®ÀåµÈ ÇÁ·ÎÆÛƼ(¶Ç´Â ¸Þ¼Òµå)·Î ½ÇÇè */
    a1.push('g');
    a1; // "asdf"
    a1.length; // 4
    
    /* ¹®ÀÚ¿­ º¯¼ö Á÷Á¢ Á¢±Ù ¹× º¯°æ */
    a1[0] = 'g';
    a1[0]; // 'a'
    
    /* ¼ýÀÚ º¯¼ö ÇÁ·ÎÆÛƼ(¶Ç´Â ¸Þ¼Òµå) È®Àå */
    q1.push = q2.push = q3.push = Array.prototype.push;
    q1.push; // function push() { [native code] }
    q2.push; // undefined
    q3.push; // undefined
    
    /* ¼ýÀÚ º¯¼ö length ÇÁ·ÎÆÛƼ È®ÀÎ ¹× º¯°æ */
    q1.length; // undefined
    q1.length = 3;
    q1.length; // 3
    
    q2.length; // undefined
    q2.length = 3;
    q2.length; // undefuned
    
    q3.length; undefined
    q3.length = 3;
    q3.length; // undefined
    
    /* È®ÀåµÈ ¸Þ¼Òµå¸¦ »ç¿ëÇÑ °æ¿ì */
    q1.push('asdfg');
    q1; // 5 { 3: "asdfg", length: 4, push: function() }
    
    /* Á÷Á¢ Á¢±ÙÇÑ °æ¿ì */
    q1[0]; // undefined
    q1[0] = 'asdf';
    q1[0]; // 'asdf';

Object Reference

    var x = null;

    window.x = null;

    var obj1 = { a: function() { return this.b; }, b: 'text message'};
    obj1.a(); // "text message"
    
    var obj2 = { a: { q : function() { return this.b }, b: 'child'}, b: 'parent'};
    obj2.a.q(); // 'child'

    (x=[].reverse)() === window; // true

    x=[].reverse;

    x === window.x; //true
    x === Array.prototype.reverse; // true

    var b = {a:[].reverse};
    b.a() === b // true

    var arr = [1, 2, 3];
    var q = arr;
    q[0] = 4;
    q; // [4, 2, 3]
    arr; // [4, 2, 3]
    arr === q; // true

    var q = [1, 2, 3];
    var a = q[0];
    a === q[0]; // true
    q[0] = 4;
    q; // [4, 2, 3]
    a === q[0]; // false
    
    var z = false;
    var x = z;
    z === x; // true
    z = true;
    z === x; // false

    var arr = [1, 2, 3];
    var obj = { a: function() { return this.length; } };
    obj.a(); // undefined
    obj.a.apply(arr); // 3

    var arr = [1, 2, 3];
    var obj = {
        a: function() {
             return (function(sl) { return this.length + sl; }).apply(arr, [this.length]);
        }
        , length: 4 };
    obj.a(); // 7

    var arr1 = [1, 2, 3];
    var arr2 = [4, 5, 6, 7, 8];
    var fn = function(v) { return this.length + v; };
    fn.binding = function(o) {
        var s = this;
        return function(bo) {
            return s.apply(bo ? bo : o, [this.length]);
        };
    };
    var obj = { a: fn.binding(arr1), length: 7 };
    obj.a(); // 10
    obj.a(arr2); // 12

    fn.binding()();

Closures

    
    fn.binding = function(obj) {
        var s = this;
        return function(bo) {
            return s.apply(bo ? bo : obj, [this.length]);
        };
    };

    obj.a; // function(bo) { return s.apply(bo ? bo : obj, [this.length]); }
    s; // undefined

    var animal = function(n, a) {
        var nick = n;
        var age = a;
        var growth = function() { return ++age; }
        return {
            setNick: function(n) { nick = n; },
            getNick: function() { return nick; },
            setAge: function(a) { age = a; },
            getAge: function() { return age; },
            getAll: function() { return [nick, age]; },
            newYear: function() { return nick + ' is now ' + growth() + ' years old'; }
        };
    };
    var dog = new animal('happy', 1);
    
    dog.nick; // undefined
    dog.age; // undefined
    
    dog.nick = 'song';
    dog.nick; // "song"
    dog.getNick(); // "happy";
    dog.setNick('MungMung');
    dog.nick; // "song"
    dog.getNick(); // "MungMung"
    
    dog.newYear(); // "MungMung is now 2 years old"
    dog.getAge(); // 2

    var el = document.getElementById('test');
    el.onclick = function() { ¡¦¡¦ };

    function setFn(id)
    {
        var el = document.getElementById(id);
        el.onclick = function() { alert(el.id); }
    }

    var el = document.getElementById('test');
    el.onclick = function() { ¡¦¡¦ };
    delete el;

    var i = 0;
    function test(){
        var i = 0; // case(3)
        return function() {
            //var j = window.i++; //case (1)
            var j = i++; // case(2)
        };
    };
    
    var fn = test();
    var t1 = new Date;
    var k = l = 0;
    
    for ( ; k++ < 200000; )
    {
        for ( ; l++ < 200000; )
        {
            fn();
        };        
    };
    alert((new Date) - t1);

Fin