How to fix error TS2322: Type 'boolean' is not assignable to type 'Promise< void>'.

I had this Promise that gave me TS-Lint errors in TypeScript.

 error TS2322: Type 'boolean' is not assignable to type 'Promise<
void>'.

This was my function:

getBookVersions(): Promise<void> {
    this.api.getBookVersions(this.book.id)
      .then(async data => {
        this.versions = data;
        return true;
      }).catch((error: Error | HttpErrorResponse) => {
      if (error instanceof HttpErrorResponse) {
        this.notificationService.showError(`Something went wrong.`);
      }
      else {
        throw error;
      }
      return false;
    });
  }

Solution

To fix typing error you need to define the function as async, it is simple like that!

Makes sense actually, a promise is always async:

async getBookVersions(): Promise<void> {
...