CODEWITHSUNDEEP
angularrxjs
cjones26
cjones26

Reputation: 3814

Why is my RxJS subscribe error handler not firing?

I am attempting to utilize Angular 2's HTTP methods in a service which is working fine until the server returns an invalid response. Here's the method code from my service:

getCalcCode(request: CalculatorRequest) {
  this.http.post(this._serviceUrl, JSON.stringify(request), this.options)
    .map((response: Response) => response.json().returnData as CalculatorResponse)
    .catch((error) => {
      return Observable.throw(error);
    })
    .subscribe((response: CalculatorResponse) => {
      if (response.returnCode === '000') {
        console.log('Code is zero!');
      }
    }, (error) => {
      console.error('Error: : ', error);
    });
}

When the server returns an invalid response, the Map operator returns undefined, therefore, when attempting to access response.returnCode from within my subscribe method, I receive:

ERROR TypeError: Cannot read property 'returnCode' of undefined

And the asynchronous code simply stops executing...the error function on subscribe is never called (EDIT: because the server is responding properly and the mapping is working properly, just to the wrong JSON format).

What can I do to ensure that errors within subscribe are caught from my error handler?

Thanks!

EDIT

After discussing this in the comments further, what I'm truly asking here is exactly how to catch errors from within my "subscribe" callback? Will I simply need to use a try/catch block?

Upvotes: 3

Views: 5336

Answers (1)

martin
martin

Reputation: 96969

The description in comments is actually a bit inaccurate. When the source emits an error then the callback to the map() operator is never called and the error is just send further (map() works only with next signals, not errors). The "one or the other, never both" rule applies only to error and complete signals, not to next signals. Of course, you can have multiple next signals.

Then it's caught by catch() and just rethrown.

  1. You don't need to be using catch() at all for this. The error is propagated as error notification already.

  2. The server probably doesn't send proper status codes so Angular HTTP service interprets them as next notifications. If the server sends for example 404 or 500 status codes it'll be automatically propagated as errors and you don't need to do anything.

Upvotes: 1

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