Prototype

★Prototype Chain

function Object1(param){

this.number = param;

}

function Object2(param){

this.string = param;

}

Object2.prototype = new Object1(10);

var myObj = new Object2("xxx");

alert(myObj.string); //xxx

alert(myObj.number); //10

alert(myObj.toString); //function(Objectに属する)

alert(myObj.dummy); //undefined

重複の場合

function User(){

this.name = 'BBB';

}

User.prototype.name = 'CCC';

var user = new User();

user.name = 'AAA';

console.log(user.name); //AAA

delete user.name;

console.log(user.name); //CCC

delete User.prototype.name;

console.log(user.name); //undefined

typeof(String.prototype); // object

typeof(User.prototype); // object

typeof(user.prototype); // undefined インスタンスの場合

prototypeによりAPIを拡張

if(!Array.prototype.pushs) {

//Array.prototype = { pushs: function(){...} }; // × 再定義できない

Array.prototype.pushs = function() { // 〇

var pos = this.length;

for(var i=0; i<arguments.length; i++) {

this[pos++] = arguments[i];

}

return this.length;

};

}

var test = ['a','b','c'];

test.pushs('d','e');

var str;

for(var key in test){

str += ' ' + key;

}

console.log(str); //0 1 2 3 4 pushs

var str;

var value;

for(var key in test){

if(test.hasOwnProperty(key)) {

str += ' ' + key;

value += ' ' + test[key];

}

}

console.log(str); //0 1 2 3 4

console.log(value); //a b c d e

★Prototype基本

function Cat(name, color){

this.name = name;

this.color = color;

}

Cat.prototype.type = "xxx";

Cat.prototype.eat = function(){...};

var cat1 = new Cat("A","white");

var cat2 = new Cat("B","black");

alert(cat1.constructor == Cat); //true

alert(cat1 instanceof Cat); //true

alert(cat1.eat == cat2.eat); //true

alert(Cat.prototype.isPrototypeOf(cat1)); //true

alert(cat1.hasOwnProperty("name")); // true

alert(cat1.hasOwnProperty("type")); // false

alert("name" in cat1); // true

alert("type" in cat1); // true