Unhandled exceptions are sometimes not surfaced

[natebosch]

What happened?

Sometimes unhandled async exceptions don't show up in the Console output area.

Steps to reproduce problem

The problem does not reproduce reliably. Refreshing the page seems to result in either having exceptions work, or not work. When they don't work they will be consistently suppressed on every run until the page is reloaded.

Additional info

Browser

Browser: Chrome

Version: 100.0.4896.75

Machine

Operating system: macOS Monterey

Version: 12.3.1

Your code

What code was in the editor, if any, when the failure occurred? You
can paste it in below:

void main() {
  throw 'sad';
}

DartPad's output

There is sometimes no output at all, or there is the expected output:

Uncaught Error: sad

In either case, the browser JS debugger console does show the error

Uncaught sad
    at Object.wrapException (<anonymous>:356:17)
    at <anonymous>:3101:23
    at _wrapJsFunctionForAsync_closure.$protected (<anonymous>:2549:15)
    at _wrapJsFunctionForAsync_closure.call$2 (<anonymous>:3484:12)
    at Object._asyncStartSync (<anonymous>:2493:20)
    at main (<anonymous>:3106:16)
    at <anonymous>:4255:7
    at <anonymous>:4238:7
    at dartProgram (<anonymous>:4249:5)
    at <anonymous>:4257:3

[parlough]

I'm going to consolidate this issue in to #3008 alongside other exception surfacing improvements. Thanks for the details!