[sly010]

Sure, we can always make up an examples.

Perhaps if you are using null to represent something explicitly in your data. But silently failing on undefined is just going to lead to an other bug somewhere else entirely and half a day of debugging.

I would much rather fail early and loudly than having to hunt down some anecdotal bug that happens every prime-th national holiday and is impossible to reproduce.

[extrapickles]

I have found it better to have UI code to use undefined over exceptions, and back-end code to use exceptions over undefined as the client should have properly formatted the request.

Having functions/methods return undefined is a huge time and complexity saver for UI code as the application could still be in the process of getting input from the user that then would be passed off to the back-end code once the user was done changing their minds. No point in having a dropdown throw an error because the user is still deciding what they want to appear in the dropdown.

[geofft]

For client-side webapps? Users are just going to hit reload and move on. For just about every website I can imagine, if your two options are to leave an extremely rare bug that's impossible to reproduce, or to effectively take the website down for all users, the former is the unambiguous right choice.

[sly010]

Well, if the bug is so hard to reproduce it would not take the website down.