Invoking private method from static method ES6

Question

I am unable to call private or non static method from static method in class, below is the example

class a {
 fun1(){
  console.log('fun1');
 }
 static staticfun(){
  console.log('staticfun');
  this.fun1();
 }
}

a.staticfun();

I am trying to expose only staticfun method which internally calls all private methods, but this gives me this.fun1 is not a function. I tried to find many ways to find it with 'this', but it does work.

How do I call private instance methods inside static methods?

There are no "private" methods in JavaScript. Do you mean *instance* methods? — Bergi, Oct 23 '18 at 10:48
It's unclear in your example, but is there a reason why you can't just make `fun1` static? — Bergi, Oct 23 '18 at 10:48
i am creating node js micro service where i am returning promise from module.exports {return new promise { promise.all().then(r=>fun2).then(r=> fun2)....at last i resolve()}} there i want to make all the promise and function to be wrapped inside class and function should not expose outside the class like modules.exports = {class a{static promise(){.....} fun1(){} fun2(){}} return a.promise()} — Tapan Dave, Oct 23 '18 at 12:53
a) avoid the [`Promise` constructor antipattern](https://stackoverflow.com/q/23803743/1048572?What-is-the-promise-construction-antipattern-and-how-to-avoid-it) b) there is [no reason to wrap anything in `class` syntax](https://stackoverflow.com/q/29893591/1048572) if you don't need multiple instances — Bergi, Oct 23 '18 at 13:13

score 5 · Answer 1 · answered Oct 23 '18 at 11:06

Another way is to call the function directly from the class prototype (meaning literally the prototype property, not __proto__), if you want to avoid instantiating it.

class a {
 fun1(){
  console.log('fun1');
 }
 static staticfun(){
  console.log('staticfun');
  this.prototype.fun1();
 }
}

a.staticfun();

Rory McCrossan · Answer 2 · 2018-10-23T10:58:31.690

4

fun1 is not a static function, so you need to define a new instance of the a class in order to call it:

class a {
  fun1() {
    console.log('fun1');
  }

  static staticfun() {
    console.log('staticfun');
    
    new this().fun1();
  }
}

a.staticfun();

You should note that this is not good practice, though. You shouldn't have a static method relying on non-static logic.

A workaround would be to pass an instance of a to the static function, but that completely defies the point of having a static method in the first place.

edited Oct 23 '18 at 10:58

answered Oct 23 '18 at 10:41

Rory McCrossan

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Why is this not ideal? – Blue Oct 23 '18 at 10:42
Expanded to add detail. – Rory McCrossan Oct 23 '18 at 10:42

omri_saadon · Answer 3 · 2018-10-23T10:47:31.963

First, read this SO question

It's possible, You can create an instance of class a and then invoke from the instance the method fun1.

Although, There is no sense to call a non-static method from a static one.

static means that this method belong to the object (not to the instance)

class a {
 fun1(){
  console.log('fun1');
 }
 static staticfun(){
  console.log('staticfun');
  const classInstance = new a()
  classInstance.fun1();
 }
}

a.staticfun();

Invoking private method from static method ES6

3 Answers3