TS1243

error TS1243: ‘static’ modifier cannot be used with ‘abstract’ modifier.

Solution

Broken Code ❌

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abstract class CustomNumber {
  abstract static getNumber(): number;
}

Your abstract class cannot define an abstract static function. You have to keep it static:

Fixed Code ✔️

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abstract class CustomNumber {
  static getNumber(): number {
    return 1337;
  };
}

error TS1243: ‘async’ modifier cannot be used with ‘abstract’ modifier.

Broken Code ❌

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abstract async goto(): Promise<void>;

Fixed Code ✔️

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abstract goto(): Promise<void>;