Singleton decorator in typescript

Question

I'm trying to use this code:

function singleton<T extends { new() }>(constructor: T): T {
    return new constructor()
}

@singleton
export default class SomeClass {
    constructor() {}

    public method(): string {
        return 'Hello!'
    }
}

console.log(SomeClass.method())

And it works. The message "Hello!" is displayed in the console. But the typescript compiler says there's error:

What's wrong?

Answer 1

Unfortunately the compiler cannot know what changes the decorator does to the class. You could try something like this:

function singleton<T>(constructor: new ()=> T): T {
    return new constructor()
}

export const SomeClass = singleton(class  {
  constructor() {}

  public method(): string {
      return 'Hello!'
  }
});

console.log(SomeClass.method())

Answer 2

Just use new before your class declaration:

export default new class {
  constructor() {}

  public method(): string {
      return 'Hello!'
  }
});