You're using poor polyfills if they use setTimeout. Good polyfills [1] use MutationObserver which uses the (a?) microtask queue. Invoking a Promise's then() ca

You're using poor polyfills if they use setTimeout. Good polyfills [1] use MutationObserver which uses the (a?) microtask queue. Invoking a Promise's then() callback synchronously is a violation of the spec. IIRC there are some tests to prevent that in the test suite. [1]: https://github.com/petkaantonov/bluebird/blob/2c9f7a44/src/schedule.js#L31 https://github.com/petkaantonov/bluebird/blob/2c9f7a44/src/s...