get TypeError: callbackFn is not a function when using decodeFromVideoDevice()

I’m on version 0.18.2 of the library, trying to use this library according to the code in this example, https://github.com/zxing-js/library/blob/master/docs/examples/multi-camera/index.html. Somehow, got the following error in the console.

TypeError: callbackFn is not a function

However, when replacing decodeFromVideoDevice() with decodeOnceFromVideoDevice(), everything is working fine.

Desktop (please complete the following information):

• OS: iOS 10.15.7
• Browser: Firefox
• Version: 81.0.1 (64-bit)

[ratiw]

Oh, sorry. That was my bad. I didn’t notice the API difference between decodeOnceFromVideoDevice() and decodeFromVideoDevice().

After calling decodeFromVideoDevice() with the callback function in the 3rd parameter, it is now working as expected.

Sorry for the trouble and really thank you for pointing me out.

Cheers,

[odahcam]

Please make sure you are correctly using the method:

            this.scanner.decodeFromVideoDevice(id, 'video', (result, err) => {
              if (err) {
                if (err && !(err instanceof ZXing.NotFoundException)) {
                  console.log('selectCamera:', err)
                }
                return;
              } // else
              this.scanSuccess(result);
            })

If you do not pass the third argument you will indeed get the callbackFn error. ImageCapture is used to check if torch is available, I think it’s better to surround that block with a try-catch and ignore this error, because browsers that doesn’t support full webrtc will throw this error and probably break code execution.