CODEWITHSUNDEEP
javascriptecmascript-6
Max Koretskyi
Max Koretskyi

Reputation: 105547

Why static methods can't be used inside instance methods or constructor

Here is the code:

class Foo {
    static m() {
        console.log('m');
    }
}
class Bar extends Foo { 
    b() {
        super.m();
    }
}

var b = new Bar();
b.b();

that throws:

Uncaught TypeError: (intermediate value).m is not a function

This type of error is generated when I attempt to use parent class static methods in an instance method or a constructor. Why?

As I understand, super refers to the Foo, and the following works OK:

class Bar extends Foo { 
    b() {
        Foo.m();
    }
}

Upvotes: 0

Views: 104

Answers (2)

Estus Flask
Estus Flask

Reputation: 223164

Because super properties refer to Foo.prototype properties in instance methods, and super properties refer to Foo static properties in static methods.

super(...) call in constructor has special meaning and does something like Foo.call(this, ...) internally.

super alone has no meaning and cannot be used as a regular variable.

It should be:

b() {
    this.constructor.m();
}

because Bar inherits m static method from Foo.

Or if it specifically should be parent class,

b() {
    super.constructor.m();
}

Upvotes: 4

Petr Volny
Petr Volny

Reputation: 569

Try to examine an instance of Foo. You will see that m is not a regular member of the Foo instance but it is "hooked" under the constructor as a public static method.

For you code to work, just change the b method definition on Bar class to:

b() {
    super.constructor.m();
}

More on this topic can be found here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes/static

Upvotes: 0

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