JavaScript type validation does not consider ES6 "extends" keywords?

Hi,

I'm recently migrating my JS code from ES5 to ES6.

In doing this, I define subclasses using ES6 "extends" keyword, instead of @extends JSDoc annotations.

Then, IDEA does not recognize a defined class (Sub_Es6Syntax in the code below) as a subclass of the base class (Base), and displays a warning on the editor.

This warning disappears if I add an @extends annotation to the definition of Sub_Es6Syntax, but it seems redundant for me.

Is it possible to use only "extends" keyword without any warnings?

Environment:

- IntelliJ IDEA 2018.2.2, Build #IU-182.4129.33, macOS

- JavaScript Language Version=ECMAScript6 in Preferences > Languages & Frameworks > JavaScript

/**
 * Base class
 */
Base = function() {};

/**
 * Subclass defined using JSDoc
 * @extends {Base}
 */
Sub_JsDoc = function() {};

/**
 * Subclass defined using ES6 syntax
 */
class Sub_Es6Syntax extends Base {}

/**
 * Some function
 * @param {Base} a
 */
function f(a) {}

f(new Sub_JsDoc());     // no warning
f(new Sub_Es6Syntax()); // !! "Argument type Sub_Es6Syntax is not assignable to parameter type Base"