Right now, if there is an exception in a .then() it is silently swallowed. I don't think we should ship 3.0.0 with that behavior.

http://jsbin.com/bodevaqive/edit?js,console

Maybe a console.warn message? We may end up yelling about rejections that might have been dealt with by a handler attached later in time.

One possible tradeoff would be to only generate the console warnings for errors that seem to be programming mistakes such as TypeError or ReferenceError. That prevents the really bad mistakes such as the example above with a typo in a function name.

For more complex cases we could recommend that people use native Promise if it's consistently available across their supported platforms, since it will be easier to debug.