Uncaught exception in watcher's callback leads to confusing error message (Assertion failed: napi_call_function...)

[jakub-g]

Issue

When the callback provided to .watch throws an exception for whatever reason, fsevents 1) crashes node process with a confusing native error message (because uncaught exception is thrown and nowhere handled), and 2) doesn't say anything about the original underlying JS error

The logged error is:

Assertion failed: (napi_call_function(env, recv, callback, 3, args, &recv) == napi_ok), function fse_dispatch_event, file ../src/fsevents.c, line 151.

which leads to think there's some issue with fsevents in native code or file system, while it's actually a boring error in the user's JS code.

Min repro:

1. create test.js

const fsevents = require('fsevents');
const stop = fsevents.watch(__dirname, () => {
    x++; // reference error: x not defined
});
setTimeout(() => {
    stop();
}, 60000);

2. node test.js
3. touch abc.txt to trigger the watcher and observe the confusing error

Workaround / solution

Wrapping the callback with try/catch fixes this. Perhaps this should be documented? (I can raise a PR).

But I think this deserves a fix in the module itself, although I'm not sure if this is feasible?