Running Vue dev, giving me promise rejection - node.js

Question

When I run vue's npm run dev, I got this error:
(node:10871) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): Error: Exited with code 3
It works fine if I run in my computer with Node 6.11.3
But fails when I deploy to AWS EC2 with Node 6.11.3, or the Latest Node 9.something
If I run with latest node, I got a detail error message:
(node:10429) UnhandledPromiseRejectionWarning: Error: Exited with code 3
at ChildProcess.cp.once.code (/home/ubuntu/loan-vue-frontend/node_modules/opn/index.js:84:13)
at Object.onceWrapper (events.js:272:13)
at ChildProcess.emit (events.js:180:13)
at maybeClose (internal/child_process.js:936:16)
at Socket.stream.socket.on (internal/child_process.js:353:11)
at Socket.emit (events.js:180:13)
at Pipe._handle.close [as _onclose] (net.js:541:12)
(node:10429) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:10429) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
I have tried just installing a new project from scratch and it works.
Then I compare the code, and I found out I have this code (in a file called 'build/dev-server.js' :
var _resolve
var readyPromise = new Promise(resolve => {
_resolve = resolve
})
console.log('> Starting dev server...')
devMiddleware.waitUntilValid(() => {
console.log('> Listening at ' + uri + '\n')
// when env is testing, don't need open it
if (autoOpenBrowser && process.env.NODE_ENV !== 'testing') {
opn(uri)
}
_resolve()
})
var server = app.listen(port)
module.exports = {
ready: readyPromise,
close: () => {
server.close()
}
}
It seems to me the readyPromise is the cause of trouble.
But the only place that call that dev-server.js is in package.json:
"scripts": {
"dev": "node build/dev-server.js",
}
I suspect
ready: readyPromise,
is not right because 'ready' may not have a catch block. but I have no clue how I can fix it if that's the case.
Any idea?