javascripterror-handlingpromisees6-promise

Should a Promise.reject message be wrapped in Error?

Using the native (ES6) Promise. Should I reject with an Error:

Promise.reject(new Error('Something went wrong'));

Or should I just reject with a string:

Promise.reject('Something went wrong');

And what is the difference in browser behaviour?

Solution

  • Yes, the rejection reason most definitely should be wrapped in new Error(). A string is not an error, when you have errors usually it means something went wrong which means you'd really enjoy a good stack trace. No error - no stack trace.

    Just like with try/catch, if you add .catch to a thrown rejection, you want to be able to log the stack trace, throwing strings ruins that for you.

    I'm on mobile so this answer is rather short but I really can't emphasize enough how important this is. In large (10K+ LoC) apps stack traces in rejections really made the difference between easy remote bug hunting and a long night in the office.