Demystifying Prototypes

Demystifying Proto........... types

null undeﬁned numberstring boolean object

b.name b[“name”] “a” in b for (var i in b) …b.hasOwnProperty(“a”) b instanceof d

functionfunction f() {};f();new f;

ObjectNumberStringBooleanFunctionArrayRegExpDate

Afunction A() {};

constructor: A Afunction A() {};

constructor: A A bfunction A() {};var b = new A;

constructor: A A x: 1 bfunction A() {};var b = new A;A.prototype.x = 1;

constructor: A A x: 1 b y: 2function A() {};var b = new A;A.prototype.x = 1;b.y = 2;

constructor: A A x: 1 c b y: 2function A() {};var b = new A;A.prototype.x = 1;b.y = 2;var c = new A;

constructor: A A x: 1 c b y: 2function A() {};var b = new A;A.prototype.x = 1;b.y = 2;var c = new A;A.prototype = {v: 1, w: 2};

v: 1 constructor: Aw: 2 A x: 1 c b y: 2 function A() {}; var b = new A; A.prototype.x = 1; b.y = 2; var c = new A; A.prototype = {v: 1, w: 2};

v: 1 constructor: Aw: 2 A x: 1 d c b y: 2 function A() {}; var b = new A; A.prototype.x = 1; b.y = 2; var c = new A; A.prototype = {v: 1, w: 2}; var d = new A;

v: 1 constructor: A w: 2 A P x: 1 d c b y: 2P.hasOwnProperty(“constructor”)“constructor” in cfor (var i in P) alert(i);c.constructorc instanceof Ad instanceof Ad.constructor

null Object Ac d

null Objectfunction A() {};function B() {};B.prototype = new A; Avar d = new B; B d

null Objectfunction A() {…};function B() {};var Z = function () {}; AZ.prototype = A.prototype;B.prototype = new Z;var d = new B; B d

null Objectfunction A() {…};function B() {};var Z = function () {}; AZ.prototype = A.prototype;B.prototype = new Z; Zvar d = new B; B d

goog.inherits = function(childCtor, parentCtor) { /** @constructor */ function tempCtor() {}; tempCtor.prototype = parentCtor.prototype; childCtor.superClass_ = parentCtor.prototype; childCtor.prototype = new tempCtor(); childCtor.prototype.constructor = childCtor;};

exports.inherits = function(ctor, superCtor) { ctor.super_ = superCtor; ctor.prototype = Object.create(superCtor.prototype, { constructor: { value: ctor, enumerable: false } });};

null Object FunctionA

JavaScript ParadoxFunction.constructor === Function

Thank Youdmitry@baranovskiy.com

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Demystifying Prototypes

by Dmitry Baranovskiy

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