obvious secrets of javascript

JavaScriptobvious secrets of

Monday, 21 December 2009

Every object (including host objects) must implement the

((Prototype)) and ((Class)) properties and the ((Get)), ((Put)),

((CanPut)), ((HasProperty)), ((Delete)), and ((DefaultValue))

methods. (Note, however, that the ((DefaultValue)) method may,

for some objects, simply throw a TypeError exception.) The value

of the ((Prototype)) property must be either an object or null, and

every ((Prototype)) chain must have finite length (that is, starting

from any object, recursively accessing the ((Prototype)) property

must eventually lead to a null value). Whether or not a native

object can have a host object as its ((Prototype)) depends on the

implementation. The value of the ((Class)) property

is defined by this specification for every

kind of built-in object. The value of the

((Class)) property of a host object may

be any value, even a value used by Monday, 21 December 2009

Every object (including host objects) must implement the

((Prototype)) and ((Class)) properties and the ((Get)), ((Put)),

((CanPut)), ((HasProperty)), ((Delete)), and ((DefaultValue))

methods. (Note, however, that the ((DefaultValue)) method may,

for some objects, simply throw a TypeError exception.) The value

of the ((Prototype)) property must be either an object or null, and

every ((Prototype)) chain must have finite length (that is, starting

from any object, recursively accessing the ((Prototype)) property

must eventually lead to a null value). Whether or not a native

object can have a host object as its ((Prototype)) depends on the

implementation. The value of the ((Class)) property

is defined by this specification for every

kind of built-in object. The value of the

((Class)) property of a host object may

be any value, even a value used by

It is a bit “cryptic”


Types


number

boolean

null

string

object

undefined


typeof

undefined "undefined"

null "object"

number "number"

boolean "boolean"

string "string"

object "object"


to Number

undefined NaN

null 0

number —

boolean true→1, false→0

string parsing

object .valueOf()


to String

undefined "undefined"

null "null"

number "5"

boolean "true"

string —

object .toString()


to Boolean

undefined FALSE

null FALSE

number 0||NaN→false

boolean —

string ""→false

object TRUE


to Object

undefined exception!

null exception!

number new Number(5)

boolean new Boolean(true)

string new String("js")

object object


5 + 4 + "px""$" + 1 + 2"4" / "2""$" + 1 - 2"web".lengthtypeof 5typeof "5"typeof {key: value}typeof nulltypeof undefinedtypeof [1, 2, 3]typeof (4 - "px")+!{}[0]


5 + 4 + "px""$" + 1 + 2"4" / "2""$" + 1 - 2"web".lengthtypeof 5typeof "5"typeof {key: value}typeof nulltypeof undefinedtypeof [1, 2, 3]typeof (4 - "px")+!{}[0]

"9px""$12"2NaN3"number""string""object""object""undefined""object""number"1


Object Properties


for in


var a = { x: 12, y: 23, r: 10, draw: function () {/*...*/}};

for (var property in a) { alert("a." + property + " = " + a[property]);}


ReadOnly

DontDelete

DontEnum

Internal


Function


var y = 1;function x() { var y = 2; return ++y;}

var z = function () { return ++y;};


function x() { var y = 2; return function () { return ++y; };}

var a = x();a();a();


typeof function (){} == "function"


Arguments


Scope, Context & “this”


function is(it) { alert(this + " is " + it);}

is("global");

is.call(5, "number");

is.apply("A", ["string"]);

alert.is = is;

alert.is("function");


Variable declaration


1 alert(b);

b = 1;

alert(a);

var a = 1;

(function () {

var x = 1;

})();

alert(x);

(function () {

y = 1;

})();

alert(y);

2

3

4


Function declaration


1

2

3

4

5

function x(a) {

return a && x(--a);

}

var x = function (a) {

return a && x(--a);

};

setTimeout(function (a) {

return a && arguments.callee(--a);

}, 1000);

var x = function y(a) {

return a && y(--a);

};

setTimeout(function y(a) {

return a && y(--a);

}, 1000);


Array declaration


var a = new Array;

var a = new Array(3);

var a = [];

var a = [undefined, undefined, undefined];

var a = [1, 2, 3, 4];


Object declaration (JSON)


var a = new Object;

var a = {};

var a = {x: 10, y: 15};

var a = { x: 10, name: "object", "font-style": "italic", getHeight: function () {/*...*/}, points: [1, 2, 3], child: {x: 10, y: 15}};


OOP


Object Owns Prototype


1

2

3

4

var mouse = {

name: "Mike",

voice: function () { alert("Squik!"); }

};

var o = new Object;

o.name = "Mike";

o.voice = function () { alert("Squik!"); };

var O = function () {

this.name = "Mike";

this.voice = function () { alert("Squik!"); };

};

var o = new O;

var O = function () {};

O.prototype.name = "Mike";

O.prototype.voice = function () { alert("Squik!"); };

var o = new O;


Inheritance


Delegation


Class

Object Object Object

Class

Object

Classic Model


Object Object Object

Object

Prototypal Model


var A = function () {};

A1


var A = function () {};A.prototype.x = 5;

A1

x: 5



var b = new A;

b

A1

x: 5



var b = new A;A.prototype.y = 6;

b

A1

x: 5y: 6



var b = new A;A.prototype.y = 6;var c = new A;

b

A1

c

x: 5y: 6



var b = new A;A.prototype.y = 6;var c = new A;b.z = 7;

b

A1

c

x: 5y: 6

z: 7



var b = new A;A.prototype.y = 6;var c = new A;b.z = 7;c.x = 4;

b

A1

c

x: 5y: 6

z: 7 x: 4




A.prototype = { w: 1, u: 2};

b

A1

c

2

x: 5y: 6

w: 1u: 2

z: 7 x: 4




A.prototype = { w: 1, u: 2};

var d = new A;

b

A1

c

2

d

x: 5y: 6

w: 1u: 2

z: 7 x: 4 —

*


Thank You


obvious secrets of javascript

Technology

var property

object properties

cryptic y object

typeof function

return function

n object

function x

value of theclass property