I think the answer to that is the same as the answer to "how do I send an email in Deno?", since this lets you run arbitrary code.
System level cron needs that feature built in because you're just telling it a command to run, and you're limited in how you deal with error and output handling of that command. That's not a problem when you're in the language you're using to define the action. Just catch your errors, or grab all STDOUT/STDERR with some solution and do with it what you want on success or error.
It's code. There is not necessarily a single solution that makes sense. The thing you're calling could throw an exception, or it could return a failure value. If it fails, you may want to set off some extra routine that retries, or perhaps you want to handle some specific errors and retry or notify, but other errors are critical and cause failure, not just notification. Having it handle those automatically is not a feature in some cases, it's a problem.
System cron is simple, by design, because as a DSL there's a benefit to not complicating it. If you're already in Javascript/Typescript, a lot of the benefits of that are mitigated by the benefits of having much more control over exactly how it functions in every care.
As an example of this, there's a bunch of cron "helpers" to deal with the shortcomings of cron's simplistic approach, such as those in moreutils[1].
P.S. Personally I wouldn't have even called this implementation cron and use the cron syntax for it, since that just makes people assume cron usage and the cron scheduling format is not an asset if you're already in a language where you could just pass in a structure with the specific fields you want set by name.
System level cron needs that feature built in because you're just telling it a command to run, and you're limited in how you deal with error and output handling of that command. That's not a problem when you're in the language you're using to define the action. Just catch your errors, or grab all STDOUT/STDERR with some solution and do with it what you want on success or error.