Steps to Reproduce

1. load the attached zul
2. open developer tool > console tab
3. click "remove" button right at the page loading within 2 seconds

Current Result

a browser could show one of the following errors:

error 1

zkmax.barscanner.wpd:1650 Uncaught TypeError: Cannot read properties of undefined (reading 'data')
at g (zkmax.barscanner.wpd:1650:31)
at n (zkmax.barscanner.wpd:1663:46)
at y (zkmax.barscanner.wpd:1664:8)
at m (zkmax.barscanner.wpd:1668:50)
at Object.start (zkmax.barscanner.wpd:1828:9)
at Object._quaggaDecode [as decode] (zkmax.barscanner.wpd:13677:14)
at zkmax.barscanner.wpd:13390:13
at zkmax.barscanner.wpd:13431:15

error 2

zkmax.barscanner.wpd:13176 Uncaught TypeError: Cannot read properties of undefined (reading 'width')
at init._setReaders (zkmax.barscanner.wpd:13176:50)
at zkmax.barscanner.wpd:13232:13
at zkmax.barscanner.wpd:13257:13

Expected Result

no error

Debug Information

• If you wait about 3 seconds and then click the remove button, the error doesn't happen.
  Because I found the reader doesn't start when a browser renders the page.

if you set a breakpoint/logpoint in the line below:

    _quaggaDecode: function _quaggaDecode(wgt, reader) {
      reader.processing = true;
      reader.start(); //set log point here    
},

Check its calling stack trace, it runs by several asynchronous function like Promise, setTimeout(), setInterval(). So because _requestCamera() is an asynchronous call, it takes 2~3 seconds to start a reader, if you remove the barcodescanner component/widget before the internal reader is ready. It will produce the js error above.

• From the use-case perspective, remove a barcodescanner immediately is a sort of unreasonable usage, so we treat this as low priority. Just record it the reference.

Workaround