property_demo.js

function TestClass (name) {
    this.name = name;
    this._somevalue = "this._somevalue";
    this._read = 0;
}

Object.defineProperty(TestClass.prototype, 'somevalue', {
    'get': function () {
        console.log(++this._read);
        return this._somevalue;
    },
    'set': function (value) {
        console.log(this._somevalue);
        console.log(this.name);
        this._somevalue = value + 5;
    }
});

var obj = new TestClass("This is my name");
obj.somevalue = 8;
console.log(obj.somevalue);