instanceof Operator
To demonstrate that instanceof checks a particular object for that particular instance (no pun intended). In JavaScript, a variable has the flexibility to have a different type throughout its life span.
by sikusikucom
JavaScript
function F() {}
function G() {}
var i = new F();
var j = new G();
console.log(i instanceof F); // true
i = j;
console.log(i instanceof F); // false
console.log(i instanceof G); // true