function MyObject() {

            Object.defineProperty(this, 'accessA', {
                set(x) {
                    if (x>0) this.a = x; // or whatever validation you want
                },
                get() { return this.a; }

            })


            }

        var obj1 = new MyObject();

        obj1.accessA=77; // call the setter
        console.log(obj1.accessA); // call the getter