How Make "typeof" On Extends In Javascript?

Example: class Foo extends Bar { } Foo typeof Bar //-> false :( How discover that Foo extend Bar?

Solution 1:

As ES6 classes inherit prototypically from each other, you can use isPrototypeOf

Bar.isPrototypeOf(Foo) // true

Alternatively just go with the usual instanceof operator:

Foo.prototype instanceof Bar // true
// which is more or (in ES6) less equivalent to
Bar.prototype.isPrototypeOf(Foo.prototype)

Solution 2:

MDN for typeof :

The typeof operator returns a string indicating the type of the unevaluated operand

you need instanceof, isPrototypeOf

class Bar{}
class Foo extends Bar {}
var n  = new Foo();

console.log(n instanceof Bar); // true
console.log(Bar.isPrototypeOf(Foo)); // true
console.log(Foo.prototype instanceof Bar); // true