Call non static method from static method javascript

I am curious as I get a "undefined is not a function" error. Consider the following class:

var FlareError = require('../flare_error.js');

class Currency {

  constructor() {
    this._currencyStore = [];
  }

  static store(currency) {
    for (var key in currency) {
      if (currency.hasOwnProperty(key) && currency[key] !== "") {

        if (Object.keys(JSON.parse(currency[key])).length > 0) {
          var currencyObject = JSON.parse(currency[key]);
          this.currencyValidator(currencyObject);

          currencyObject["current_amount"] = 0;

          this._currencyStore.push(currencyObject);
        }
      }
    }
  }

   currencyValidator(currencyJson) {
    if (!currencyJson.hasOwnProperty('name')) {
      FlareError.error('Currency must have a name attribute in the json.');
    }

    if (!currencyJson.hasOwnProperty('description')) {
      FlareError.error('Currency must have a description attribute in the json.');
    }

    if (!currencyJson.hasOwnProperty('icon')) {
      FlareError.error('Currency must have a icon attribute in the json.');
    }
  }

  static getCurrencyStore() {
    return this._currencyStore;
  }

};

module.exports = Currency;

Refactoring aside, the issue is on the line: this.currencyValidator(currencyObject); I get the error "undefined is not a function"

I assume this is because I have a static method who's internals call a non static method? Would that non static method have to be static? and if so does the concept of this.methodName still work?

asked Oct 27, 2015 at 15:17

2

No, a static method cannot call a non-static method.

Consider that you have objects a and b, both instances of Currency. currencyValidator exists on those two objects. Now store() belongs to the class Currency itself, not one of those objects. So, in Currency.store(), how does it know which object to call currencyValidator() on? The simple answer is it doesn't so it can't. This is one of the pitfalls of using static methods and one of the reasons people often urge against them.

Regardless, you can get around this by passing a into Currency.store(), and calling a.currencyValidator() instead.

answered Oct 27, 2015 at 15:23

JoshJosh

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0

It makes no sense to call a non-static function from a static one, in any language. Static (in this context) means that it's basically outside of the object, independent in all but name. It's not tied to any instance and thus there's no this or self to call non-static (ie member) fields.

answered Oct 27, 2015 at 15:20

BlindyBlindy

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3

No, in general static methods cannot call instance methods. It makes little sense to be able to do so.

The only caveat is that there is nothing stopping a static method instantiating an instance of a class, at which point it can call the instance methods in the usual way.

answered Oct 27, 2015 at 15:21

JamiecJamiec

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A static method provides NO reference to an instance of its class (it is a class method) hence, no, you cannot call a non-static method inside a static one.

Of course you may either

• Create an object of the class inside the static method and then call the non-static method using such an object.

or

• Pass an instance of the class as static method parameter (and then, again, use such instance for invoking the non-static method).

Due to the vagueness of your question there can be many other ways (for instance, calling a non-static method of an object of a completely unrelated class).

Providing examples is left as an exercise.

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