callFunction3.js

var myObj = {
	value : 0,
	increment : function(inc) {
		this.value += typeof inc === 'number' ? inc : 1;
	}
};

myObj.increment();
console.log(myObj.value); // 1

myObj.increment(2);
console.log(myObj.value); // 3


var add = function(a, b) {
	return a + b;
}

myObj.double = function() {
	var that = this;

	var helper = function() {
		that.value = add(that.value, that.value);
	};

	// 関数呼び出し
	helper();
}

// メソッド呼び出し
myObj.double();
console.log(myObj.value); // 6