JavaScript instanceof运算符在应该为false时返回true？

Question

I was working on a JavaScript application and came over this weird behavior.
Can anyone please explain to me why

function BaseClass() {}
function ClassOne() { this.bar = "foo"; }
function ClassTwo() { this.foo = "bar"; }

var base = new BaseClass();
ClassOne.prototype = base;
ClassTwo.prototype = base;

var one = new ClassOne();
var two = new ClassTwo();
one instanceof ClassTwo && two instanceof ClassOne;
// The line above will return true, but i think it should return false,
// because obviously one is not an instance of ClassTwo!

Answer 1

Both one and two have the same prototype (constructor BaseClass ). Object.getPrototypeOf(one) === Object.getPrototypeOf(two) .

Instead of "recycling" new BaseClass in base , use:

// var base = new BaseClass(); <-- No!
ClassOne.prototype = new BaseClass();
ClassTwo.prototype = new BaseClass();