// 基类

var BaseCalculator = function(){

	this.decimalDigits = 2;

};

// public

BaseCalculator.prototype.add = function(x, y) {

	return x + y;

}

// public

BaseCalculator.prototype.subtract = function(x, y) {

	return x - y;

}

// 子类

var Calculator = function() {

	this.tax = 5;

};

// 覆盖重写

Calculator.prototype.add = function(x, y) {

	return x + y + this.tax;

}

// 实例继承

Calculator.prototype = new BaseCalculator();

var calc = new Calculator();

console.log(calc.add(1,1));

console.log(calc.decimalDigits);

/* 原型继承。不让子类訪问基类的属性

Calculator.prototype = BaseCalculator.prototype;

var calc = new Calculator();

console.log(calc.add(1,1));

console.log(calc.decimalDigits);// 无法訪问

*/

// 原型链遍历从自身属性到原型链，从下向上遍历，到Object.prototype 结束。

Object.prototype.bar = 1;

var foo = {moo:2};

for(var i in foo) {

	console.log(i);

}

// foo bar

for(var i in foo) {

	if(foo.hasOwnProperty(i)) {

		console.log(i);

	}

}

// moo