Obvious Secrets of JavaScript

obvious secrets of

JavaScript

Monday, 21 December 2009

E very object (including host objects) must implement the
e)) and ((Class)) propertie s and the ((Get)), ((Put)),
((Prototyp
t)), ((HasProperty)), ((Dele te)), and ((DefaultValue))
((CanPu
. (Note, however, that the ((D efaultValue)) method may,
methods exception.) The value
for some objects , simply throw a TypeError
Prototype)) property must be either an object or null, and
of the ((
Prototype)) chain must have finite length (that is, starting
every ((
y object, recursively access ing the ((Prototype)) property
from an
entually lead to a null val ue). Whether or not a native
must ev
an have a host object as its ((Prototype)) depends on the
object c
implementation.
The value of the ((Class)) property
is defined by this specification for every
kind of built-i n object. The value of the
((Class)) prop erty of a host object may
be any value , even a value used by

E very object (including host objects) must implement the
e)) and ((Class)) propertie s and the ((Get)), ((Put)),
((Prototyp
t)), ((HasProperty)), ((Dele te)), and ((DefaultValue))
((CanPu
. (Note, however, that the ((D efaultValue)) method may,
methods exception.) The value
for some objects , simply throw a TypeError
Prototype)) property must be either an object or null, and
of the ((
Prototype)) chain must have finite length (that is, starting
every ((
ing the ((Prototype)) property
from an It is a bit “cryptic”
y object, recursively access
entually lead to a null val ue). Whether or not a native
must ev
an have a host object as its ((Prototype)) depends on the
object c
implementation.
The value of the ((Class)) property
is defined by this specification for every
kind of built-i n object. The value of the
((Class)) prop erty of a host object may
be any value , even a value used by

Types


number string

boolean object

null 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".length
typeof 5
typeof "5"
typeof {key: value}
typeof null
typeof undefined
typeof [1, 2, 3]
typeof (4 - "px")
+!{}[0]


5 + 4 + "px" "9px"
"$" + 1 + 2 "$12"
"4" / "2" 2
"$" + 1 - 2 NaN
"web".length 3
typeof 5 "number"
typeof "5" "string"
typeof {key: value} "object"
typeof null "object"
typeof undefined "undefined"
typeof [1, 2, 3] "object"
typeof (4 - "px") "number"
+!{}[0] 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 DontEnum

DontDelete 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


alert(b);
1 b = 1;

alert(a);
2 var a = 1;

(function () {
3 var x = 1;
})();
alert(x);

(function () {
4 y = 1;
})();
alert(y);


Function declaration


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


Inheritance


Delegation


Classic Model

Class

Object
Class

Object Object Object


Prototypal Model

Object

Object Object Object


var A = function () {};

1 A


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

1 A


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

var b = new A;
1 A

b


x: 5
var A = function () {}; y: 6
A.prototype.x = 5;

var b = new A;
A.prototype.y = 6; 1 A

b


x: 5
A.prototype.x = 5;

var b = new A;
var c = new A;

b c


x: 5
A.prototype.x = 5;

var b = new A;
var c = new A;
b.z = 7;

b c

z: 7


x: 5
A.prototype.x = 5;

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

b c

z: 7 x: 4


x: 5 w: 1
var A = function () {}; y: 6 u: 2
A.prototype.x = 5;

var b = new A;
A.prototype.y = 6; 1 A 2
var c = new A;
b.z = 7;
c.x = 4;

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

z: 7 x: 4


x: 5 w: 1
var A = function () {}; y: 6 u: 2
A.prototype.x = 5;

var b = new A;
A.prototype.y = 6; 1 A 2
var c = new A;
b.z = 7;
c.x = 4;
*
A.prototype = {
w: 1,
u: 2 b c d
};

var d = new A; z: 7 x: 4 —


Thank You


Obvious Secrets of JavaScript

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