CODEWITHSUNDEEP
javascriptclassasynchronousecmascript-6
Kevin Gilbert
Kevin Gilbert

Reputation: 1022

Is that class method async ? (no instance)

I have a very simple question, I've been looking around but I can't find the solution.

Take that code :

class Foo {
  bar = () => {
      return 'string'
  }

  baz = async() => {
      return 'promise'
  }
}

I want to know if a specific method of a class is async or not.

isAsync(Foo, 'bar') // false
isAsync(Foo, 'baz') // true

the thing is ... I DO NOT want to instantiate it. All the solutions I found uses "getOwnPropertyNames" on a class instance to get the functions.

Is it possible ?

Thanks ! 🍺

Upvotes: 0

Views: 102

Answers (2)

Felix Kling
Felix Kling

Reputation: 816790

the thing is ... I DO NOT want to instantiate it. All the solutions I found uses "getOwnPropertyNames" on a class instance to get the functions.

Is it possible ?

In your specific example, bar and baz are instance class fields. It's the same as writing

class Foo {
  constructor() {
    this.bar = () => {
       return 'string'
    };

    this.baz = async() => {
        return 'promise'
    };
  }
}

The properties (and functions) don't exist until you actually created an instance of the class.

So the answer for this specific case is no.

If you declare the functions as "normal" class methods then you can simply look at the constructor function's prototype property.

Upvotes: 1

Dmitry Reutov
Dmitry Reutov

Reputation: 3032

// the most simple way is
const isAsync = (someClass, name) => {
  if (name in someClass.prototype) 
    return someClass.prototype[name][Symbol.toStringTag] === 'AsyncFunction'

  const newInstance = new someClass()
  if (name in newInstance)
    return newInstance[name][Symbol.toStringTag] === 'AsyncFunction'
}

Upvotes: 1

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