Discovering the method to access a local function within a static function in Javascript ES6 (ES2015) or Typescript

Is there a way to access the non-static "foo2" method from inside the static "bar" method? So far, I'm only able to access the "foo1" and "foo3" methods. Can anyone provide guidance on how to achieve this?

let foo1 = () => {
    alert('foo1’);
  };

class ABC extends Component {

  static bar() {
      foo1(); //works fine

      foo2; //throws error "Can't find variable foo2"

      foo2(); //throws error "Can't find variable foo2"

      this.foo2(); //throws error "this.foo2 is not a function"

      this.foo2; //no error but no alert displayed

      ABC.foo3() //works fine
  }

  foo2 = () => {
      alert('foo2');
  };

  static foo3 = () => {
      alert('foo3');
  };

}

module.exports = ABC;

Answer №1

Caution: It is not recommended to access instance-methods from static-methods as it may lead to confusion for other developers. Try to avoid this practice, but if necessary, ensure that your code is well-documented and clearly explains its functionality.

If you need to call a method from a static method within the context of an object, you can achieve this by using the call method:

class ABC extends Component {
    static bar () {
      this.foo();
    }
    foo () {
      // function body
    }
}

let instance = new ABC();
ABC.bar.call(instance);

Alternatively, you can use bind when passing the function as a callback, or "pre-bind" it like so:

let instance = new ABC();
setTimeout(ABC.bar.bind(instance), 1000);

Please note: By default, the reference of this in a static method points to the class itself, and not an instance. After binding, it will refer to an instance. If you wish to call another static method from the first static method, specify the full class name.

static bar () {
  this.foo();
  ABC.someOtherStaticMethod();
}

Additionally: If you are using Typescript, you may encounter an error when referencing instance-methods, as this in a static method refers to the class. To resolve this, you can cast the type of this to any:

static bar () {
  (<any>this).foo();
}

In this scenario, you are instructing the Typescript compiler to treat this as an unknown entity, allowing you to eliminate compile-time errors.

Answer №2

It is impossible to call instance methods from a static method in any programming language due to the nature of static methods. Since there is only one static method in a class, it cannot determine which specific instance (this) to refer to.

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