Obvious Secrets of JavaScript

obvious secrets of JavaScript Monday, 21 December 2009

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 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 (( 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 Monday, 21 December 2009

Types Monday, 21 December 2009

number string boolean object null undefined Monday, 21 December 2009

typeof undefined "undefined" null "object" number "number" boolean "boolean" string "string" object "object" Monday, 21 December 2009

to Number undefined NaN null 0 number — boolean true→1, false→0 string parsing object .valueOf() Monday, 21 December 2009

to String undefined "undefined" null "null" number "5" boolean "true" string — object .toString() Monday, 21 December 2009

to Boolean undefined FALSE null FALSE number 0||NaN→false boolean — string ""→false object TRUE Monday, 21 December 2009

to Object undefined exception! null exception! number new Number(5) boolean new Boolean(true) string new String("js") object object Monday, 21 December 2009

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] Monday, 21 December 2009

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 Monday, 21 December 2009

Object Properties Monday, 21 December 2009

for in Monday, 21 December 2009

var a = { x: 12, y: 23, r: 10, draw: function () {/*...*/} }; for (var property in a) { alert("a." + property + " = " + a[property]); } Monday, 21 December 2009

ReadOnly DontEnum DontDelete Internal Monday, 21 December 2009

Function Monday, 21 December 2009

var y = 1; function x() { var y = 2; return ++y; } var z = function () { return ++y; }; Monday, 21 December 2009

function x() { var y = 2; return function () { return ++y; }; } var a = x(); a(); a(); Monday, 21 December 2009

typeof function (){} == "function" Monday, 21 December 2009

Arguments Monday, 21 December 2009

Scope, Context & “this” Monday, 21 December 2009

function is(it) { alert(this + " is " + it); } is("global"); is.call(5, "number"); is.apply("A", ["string"]); alert.is = is; alert.is("function"); Monday, 21 December 2009

Variable declaration Monday, 21 December 2009

alert(b); 1 b = 1; alert(a); 2 var a = 1; (function () { 3 var x = 1; })(); alert(x); (function () { 4 y = 1; })(); alert(y); Monday, 21 December 2009

Function declaration Monday, 21 December 2009

Array declaration Monday, 21 December 2009

var a = new Array; var a = new Array(3); var a = []; var a = [undefined, undefined, undefined]; var a = [1, 2, 3, 4]; Monday, 21 December 2009

Object declaration (JSON) Monday, 21 December 2009

OOP Monday, 21 December 2009

Object Owns Prototype Monday, 21 December 2009

Inheritance Monday, 21 December 2009

Delegation Monday, 21 December 2009

Classic Model Class Object Class Object Object Object Monday, 21 December 2009

Prototypal Model Object Object Object Object Monday, 21 December 2009

var A = function () {}; 1 A Monday, 21 December 2009

var A = function () {}; x: 5 A.prototype.x = 5; 1 A Monday, 21 December 2009

var A = function () {}; x: 5 A.prototype.x = 5; var b = new A; 1 A b Monday, 21 December 2009

x: 5 var A = function () {}; y: 6 A.prototype.x = 5; var b = new A; A.prototype.y = 6; 1 A b Monday, 21 December 2009

x: 5 var A = function () {}; y: 6 A.prototype.x = 5; var b = new A; A.prototype.y = 6; 1 A var c = new A; b c Monday, 21 December 2009

x: 5 var A = function () {}; y: 6 A.prototype.x = 5; var b = new A; A.prototype.y = 6; 1 A var c = new A; b.z = 7; b c z: 7 Monday, 21 December 2009

x: 5 var A = function () {}; y: 6 A.prototype.x = 5; var b = new A; A.prototype.y = 6; 1 A var c = new A; b.z = 7; c.x = 4; b c z: 7 x: 4 Monday, 21 December 2009

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 Monday, 21 December 2009

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 — Monday, 21 December 2009

Thank You Monday, 21 December 2009

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Obvious Secrets of JavaScript

by Dmitry Baranovskiy on Dec 20, 2009

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