Unhandled promise rejection: TypeError: Cannot read property 'attachData' of undefined

Hello!

As I run tests for my Angular app, I am encountering this error Unhandled promise rejection: TypeError: Cannot read property 'attachData' of undefined in components that aren’t using the barcode scanner component I created using this library.

Here’s an example of the error message I am seeing while I run the tests. This is an example where it’s occurring in a component that isn’t using the barcode scanner.

Any suggestions on how to resolve this? Am I not catching a promise correctly somewhere?

[ericblade]

right, like I’m curious why Angular is causing it to occur in different parts of the code. Even if it’s being used correctly, is OP structuring something so that Angular would be calling init() and start() several times unexpectedly?

Either way, though, it sounds like it’s probably a good idea to either make start() throw if init() hasn’t been completed, and/or if start() receives a configuration block, then do init() and chain to start() when it’s done…

[undamaged18]

For root cause, Based on what I can see the error is being thrown because the Quagga code can’t find the element it trying to attach to, which is the correct behaviour of the code and I’m not convinced that the issue lies with Quagga without actual code examples from the OP

Noting that this is only speculation, only thing I can think of which would cause what the OP is seeing is they start the camera and then the test moves on to other components of Angular, without more information from the OP not much I could comment on the exact nature of the error

But could be fixed of calling ngOnDestory() to stop() the camera when the component changes and the barcode scanner is no longer being used

  ngOnDestroy() {
    Quagga.stop();
  }

There could also be something in the OP’s code is trying to restart the camera and could be a simple fix by adding some logic to check if the element exists if (this.elRef.nativeElement.querySelector('#camera') !== null) { ... }

Again some comments from the OP would help get to the root cause as I have not been able to replicate the issue other than calling start() outside of the init() callback