These methods are event oriented and should not have been using promises.

A promise is intended to only be resolved once, however this library is expecting to resolve them multiple times.
https://stackoverflow.com/questions/20328073/is-it-safe-to-resolve-a-promise-multiple-times

these API's need to be altered to queue.onIdle(() => { }); and register an array of callbacks,
or ideally, use an EventEmitter style API and do queue.on('idle', () => { });

these existing API's can be altered to forward to the new preferred API by returning something like
return {
then(cb) { this.on('idle', cb); return this; }
catch (e) { } //unused, but part of promise expectation
}