function Foo() {}
Foo.prototype.x = 1;
var f = new Foo();
console.log(f.x);
console.log(f.hasOwnProperty('x')); //false
console.log(f._proto_.hasOwnProperty('x')); // 老师，这个地方报错诶 Uncaught TypeError: Cannot read property 'hasOwnProperty' of undefined
console.log(f.__proto__.hasOwnProperty('x'));
_proto_ -> __proto__
。。。。。。。