Question

84

Typescript returning boolean after promise resolved

rated 0 times [ 91] [ 7] / answers: 1 / hits: 79360 / 7 Years ago, sun, august 13, 2017, 12:00:00

I'm trying to return a boolean after a promise resolves but typescript gives an error saying

A 'get' accessor must return a value.

my code looks like.

get tokenValid(): boolean {

    // Check if current time is past access token's expiration

    this.storage.get('expires_at').then((expiresAt) => {

      return Date.now() < expiresAt;

    }).catch((err) => { return false });

}

This code is for Ionic 3 Application and the storage is Ionic Storage instance.

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sandra

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3 Years ago

answered 7 Years ago jackie · Accepted Answer

You can return a Promise that resolves to a boolean like this:

get tokenValid(): Promise<boolean> {

  // |

  // |----- Note this additional return statement. 

  // v

  return this.storage.get('expires_at')

    .then((expiresAt) => {

      return Date.now() < expiresAt;

    })

    .catch((err) => {

      return false;

    });

}

The code in your question only has two return statements: one inside the Promise's then handler and one inside its catch handler. We added a third return statement inside the tokenValid() accessor, because the accessor needs to return something too.

Here is a working example in the TypeScript playground:

class StorageManager { 



  // stub out storage for the demo

  private storage = {

    get: (prop: string): Promise<any> => { 

      return Promise.resolve(Date.now() + 86400000);

    }

  };



  get tokenValid(): Promise<boolean> {

    return this.storage.get('expires_at')

      .then((expiresAt) => {

        return Date.now() < expiresAt;

      })

      .catch((err) => {

        return false;

      });

  }

}



const manager = new StorageManager();

manager.tokenValid.then((result) => { 

  window.alert(result); // true

});