function MyObject(){
  var privateVariable = 10;
  function privateFunction(){
    return false;
  }
  this.publicMethod = function(){
    privateVariable ++;
    return privateFunction();
  };
}  
var x = new MyObject();
console.log(x.publicMethod()) ;//false

(function(){
  var privateValue = 10;
  function privateFunction(){
    return false;
  }
  
  MyObject = function(){}; //没有var 属于全局变量，严格模式下会报错
  
  MyObject.prototype.publicMethod = function(){
    privateValue ++;
    return privateFunction();
  };
})();

var instance = new MyObject();
console.log(instance.publicMethod());

Obj = function(){};

(function(){
  var x = 10;
  function y(){
    return x + 10;
  }

  Obj.prototype.say = function(){
    console.log(y());
  };
})()

var ins = new Obj();
ins.say();