Angular http guide error handling - mistake?

Question

I read this guide here: https://angular.io/guide/http#getting-error-details

And in the snippet the guide provides the code tries to differentiate: a) client side error (like no connection etc) and b) backend responses (see code in the guide or in the pic below).

I did implement this code for my case and surprisingly when I do offline mode in Chrome dev tools (set offline flag) - I catch those errors as "backend" errors while I thought it should be the client error.

See below what error I get and my code snippet (same as in the guide):

This is a snapshot of the console.log - where clearly this message "Backend returned..." should have been shown if there was in fact server side response.

What am i missing here? Is this code: err.error instanceof Error - even valid?

Max Koretskyi · Accepted Answer · 2018-01-08 08:44:02Z

2

The example seems to be a little outdated. HttpClient uses XHR backend under the hood and what the documentation refers to as client side error is XHR errors delivered through the error callback:

var oReq = new XMLHttpRequest();
oReq.error = handler()

According to the spec, XHR errors are instances of ProgressEvent interface, so the this check should be added:

if (e.error instanceof Error || e.error instanceof ProgressEvent) { }

edited Jan 8, 2018 at 8:44

answered Jan 8, 2018 at 8:31

Max Koretskyi

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5 Comments

Sergey Rudenko Over a year ago

Hey thank you for your response, I did see the ProgressEvent was logged during those errors and was wondering!:) So am I right to say that current guide at angular.io is not up to date then?

Max Koretskyi Over a year ago

@SergeyRudenko, yeah, I created a pull request.

hjchin Over a year ago

As of today, e.error instanceof ProgressEvent returns false. I wonder why. Based on the debug watch, it is a ProgressEvent but the statement e.error instanceof ProgressEvent returns false!

Max Koretskyi Over a year ago

@hjchin, interesting, thanks. Can you maybe create a stackblitz demo? I just checked the spec and it hasn't changed so an error should be an instance of ProgressEvent

Harel M Over a year ago

I have the same issue, console.log of e.error is showing a ProgressEvent but instanceof is returning false. see github.com/IsraelHikingMap/Site/issues/1660 @MaxKoretskyi did you find a solution for this

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