function foo(){}foo.prototype.z=3;var obj=new foo();obj.y=2;obj.x=1;//调用obj.x;//1obj.y;//2obj.z;//3typeof obj.toString;//'function''z' in obj;//trueobj.hasOwnProperty('z');//falseobj.z=5;obj.z;//5'z' in obj;//trueobj.hasOwnProperty('z');//truefoo.prototype.z;//3