function A() {
        this.a = 1;
        this.f = function () {
            this.a = 2;
            return this.a;
        }
    }
    var a = new A();
    alert(a.a)
    a.f();
    alert(a.a)

------解决方案--------------------
function A(){
  this.a = 1;
  this.f = new B();
}
function B(){
 this.a = 2;
}

var temp = new A();
    alert( temp.f.a);

------解决方案--------------------
探讨

你这是要从新给a赋值吗？
是的话可以这样
this.a = 2;  
return this.a;


------解决方案--------------------
JScript code




        function A() {
            this.a = 1;
            var sender = this;
            this.f = function () {
                sender.a = 2;
                
            }
        }

        var c = new A(); 
        c.f();
        alert(c.a);// 为2