I have the following TypeScript method which returns a promise:

public loadSavedLogin(): ng.IPromise<MyApp.Models.User> {
   return this._myAppService.getUser(this.savedUserId).then((result: MyApp.Models.User) => {
       if (result) {
          this.userId = result.UserID;
          this.userName = result.UserName;
        }
        return result;
     }, (error) => {
           this._isAuthError = true;
           return  error;
     }
  );
}

The problem I have is in the promise's error callback. The upstream calls to this method also rely on a promise so if the error does not bubble up correctly, the upstream promise doesn't function correctly. I found a hackish solution:

(error) => {

      try {
             this._isAuthError = true;
             return error;
           } catch (e) {
              //If any error occurred above make sure to still throw
              throw error;
           } finally {
                //Allow upstream promises to continue as expected
                throw error;
           }
 }

This works but looks, feels, and is probably all wrong. I feel like I'm missing a proper implementation when handling and bubbling errors in a promise. There has to be a more proper/correct way of handling the error function in this promise as I've done, and yet still allow upstream promise's making a call to this method to work properly as well when handling their own error function.

How do I get the error to bubble without the series of hackish throw statements?

Note: It seems redundant to return the error and throw as well, but the IPromise interface I'm using will not pile if I don't return a value. This is why I return and throw the error.

Note: I read a ton of the questions on handling errors with promises, but none of them are answering the question as I'm asking in regards to preventing the hackish approach I've taken.

I have the following TypeScript method which returns a promise:

public loadSavedLogin(): ng.IPromise<MyApp.Models.User> {
   return this._myAppService.getUser(this.savedUserId).then((result: MyApp.Models.User) => {
       if (result) {
          this.userId = result.UserID;
          this.userName = result.UserName;
        }
        return result;
     }, (error) => {
           this._isAuthError = true;
           return  error;
     }
  );
}

The problem I have is in the promise's error callback. The upstream calls to this method also rely on a promise so if the error does not bubble up correctly, the upstream promise doesn't function correctly. I found a hackish solution:

(error) => {

      try {
             this._isAuthError = true;
             return error;
           } catch (e) {
              //If any error occurred above make sure to still throw
              throw error;
           } finally {
                //Allow upstream promises to continue as expected
                throw error;
           }
 }

This works but looks, feels, and is probably all wrong. I feel like I'm missing a proper implementation when handling and bubbling errors in a promise. There has to be a more proper/correct way of handling the error function in this promise as I've done, and yet still allow upstream promise's making a call to this method to work properly as well when handling their own error function.

How do I get the error to bubble without the series of hackish throw statements?

Note: It seems redundant to return the error and throw as well, but the IPromise interface I'm using will not pile if I don't return a value. This is why I return and throw the error.

Note: I read a ton of the questions on handling errors with promises, but none of them are answering the question as I'm asking in regards to preventing the hackish approach I've taken.

• javascript
• angularjs
• typescript

2 Answers 2

I am not conversant with TypeScript, but here is a javascript solution, where you use $q.reject

.then(function() {}, 
      function(error) {
          this._isAuthError = true; 
          return $q.reject(error); 
      });`

Just throw the error instead of ever returning it:

public loadSavedLogin(): ng.IPromise<MyApp.Models.User> {
   return this._myAppService.getUser(this.savedUserId).then((result: MyApp.Models.User) => {
       if (result) {
          this.userId = result.UserID;
          this.userName = result.UserName;
        }
        return result;
     }, (error) => {
           this._isAuthError = true;
           throw  error;
     }
  );
}

Note that a valid return (i.e. not returning a promise / rejected promise) from a rejection handler makes the next promise in the chain fulfilled.