Ok, thanks, I get it now. In my case a macro transforms the body of each callback to catch exceptions and pass them back as error args through the callback chain. So in your example, there would be a generated try-catch around the JSON.parse(data). I forgot this detail (sign of a successful abstraction?) and it does seem an example of something macros can do that functions cannot.
Re null reference checks, to get behavior analogous to a null exception you have not only to check for null, but also pass back an explicit error if you find it. That's a lot more work than adding in an extra question mark. Null checks that do nothing but not crash are a mixed blessing; 90+% of the time they do what you want, but when they don't, you get a silent failure and a debugging goose chase. I'd be surprised if you told me that that never happens.
I took a look at Node.js domains and they do seem really complicated. If I were working in Javascript instead of having control over the language, I doubt I would use them; I would probably just crash-and-restart as one of the other commenters described. That's not a good solution, but probably the best tradeoff given the alternatives.
Our use-case for domains is to allow the process to finish serving its other in-progress reqs before crashing. When an error occurs, we stop accepting new connections in that process, give them 10-15 seconds to complete, and then do the crash-and-restart cycle.
That said, we get very thorough testing from our large user base, and we quickly fix crashers. Our server proc crash rate is almost 0, brought up by occasional spikes on releases.
Re null reference checks, to get behavior analogous to a null exception you have not only to check for null, but also pass back an explicit error if you find it. That's a lot more work than adding in an extra question mark. Null checks that do nothing but not crash are a mixed blessing; 90+% of the time they do what you want, but when they don't, you get a silent failure and a debugging goose chase. I'd be surprised if you told me that that never happens.
I took a look at Node.js domains and they do seem really complicated. If I were working in Javascript instead of having control over the language, I doubt I would use them; I would probably just crash-and-restart as one of the other commenters described. That's not a good solution, but probably the best tradeoff given the alternatives.