javascript - “await this.method();” doesn’t work in static method - Stack Overflow

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I know of the ES6 await feature and I’d like to use it in a function I created in a class.

It works well, but when the function is a static function, it doesn’t. Is there any reason for that? Also, what will be the right way to be able to use await inside a static function?

class MyClass {
  resolveAfter2Seconds() {
    return new Promise(resolve => {
      setTimeout(() => {
        resolve('resolved');
      }, 2000);
    });
  }

  static async asyncCall() {
    console.log('calling');
    var result = await this.resolveAfter2Seconds();
    console.log(result);
    // expected output: "resolved"
  }
}

MyClass.asyncCall();

I know of the ES6 await feature and I’d like to use it in a function I created in a class.

It works well, but when the function is a static function, it doesn’t. Is there any reason for that? Also, what will be the right way to be able to use await inside a static function?

class MyClass {
  resolveAfter2Seconds() {
    return new Promise(resolve => {
      setTimeout(() => {
        resolve('resolved');
      }, 2000);
    });
  }

  static async asyncCall() {
    console.log('calling');
    var result = await this.resolveAfter2Seconds();
    console.log(result);
    // expected output: "resolved"
  }
}

MyClass.asyncCall();

• javascript
• static
• async-await
• es6-promise
• es6-class

Share Improve this question Follow edited Apr 3, 2018 at 0:22 Sebastian Simon 19.5k88 gold badges6161 silver badges8484 bronze badges asked Apr 3, 2018 at 0:02 John DavidJohn David 77222 gold badges99 silver badges2121 bronze badges 1

• It should work. In what way does it not work? – Get Off My Lawn Commented Apr 3, 2018 at 0:05

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2 Answers 2

Sorted by: Reset to default 4

You can use await just fine in a static function. That is not your issue.

BUT, this in a static function is MyClass so this.someMethod() is looking for another static method, not an instance method and resolveAfter2Seconds() is an instance method, not a static method so this.resolveAfter2Seconds() won't find that method because that's like calling MyClass.resolveAfter2Seconds() which doesn't exist.

If you also make resolveAfter2Seconds() be static, then it would probably work because this inside asyncCall() is MyClass so this.resolveAfter2Seconds() is looking for another static method.

This should work where you make resolveAfter2Seconds also be static:

class MyClass {

  static resolveAfter2Seconds() {
    return new Promise(resolve => {
      setTimeout(() => {
        resolve('resolved');
      }, 2000);
    });
  }

  static async asyncCall() {
    console.log('calling');
    var result = await this.resolveAfter2Seconds();
    console.log(result);
    // expected output: "resolved"
  }
}

Or, you could reach into the prototype and call it from there because it is actually a static method (doesn't reference this at all):

  static async asyncCall() {
    console.log('calling');
    var result = await MyClass.prototype.resolveAfter2Seconds();
    console.log(result);
    // expected output: "resolved"
  }

You're calling await this.resolveAfter2Seconds(); as if the this was an instantiation of MyClass, but in the context that your'e calling it, it isn't - resolveAfter2Seconds is a method on the prototype of MyClass, it's not a property of the class itself. Call the prototype method instead:

class MyClass {
  resolveAfter2Seconds() {
    return new Promise(resolve => {
      setTimeout(() => {
        resolve('resolved');
      }, 2000);
    });
  }
  static async asyncCall() {
    console.log('calling');
    var result = await this.prototype.resolveAfter2Seconds();
    console.log(result);
    // expected output: "resolved"
  }

}
MyClass.asyncCall();

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