Display warning messages in Node.js apps when rejected promises are not handled

promise-unhandled-rejection.js

let rejectionTimeouts = new WeakMap()

function displayError({ stack }) {
	process.stderr.write(stack + '\n')
}

process.on('unhandledRejection', (err, promise) => {
	rejectionTimeouts.set(promise, setTimeout(() => displayError(err), 200))
})

process.on('rejectionHandled', promise => {
	clearTimeout(rejectionTimeouts.get(promise))
	rejectionTimeouts.delete(promise)
})