How to properly throw an error and exit with a specific exit code?

[tukusejssirs]

For example, when a parse method fails, I want to output an error (using a logger) and exit with an exit code. I can exit using process.exit(2) in the parse method, but is it the best way?

Is there some lifecycle events (similart to those of Nest)? Those need to be enabled using app.enableShutdownHooks() in main.ts file, however, there seems no way to do the same with CommandFactory.run().

It might be a good idea to somehow abstract this and define the exit codes in Nest Commander and append them to the help of each command. I’d suggest to output them all in global help, but output only a subset of exit codes for (sub-) commands (output only those that are used by a command). However, if we define an exit cope in decorators, we need to reference them in the methods themselves, which might complicate the implementation a bit.

[jmcdo29]

I have this mentioned in the docs that there's nothing specific that nest-commander does, it's all at the commander level and you can pass your own error handler through the CommandFactory.run(). method.

I'll think if there's a way to abstract an error handler out of this to make it easier to work with

[tukusejssirs]

Well, yeah, I could use errorHandler, but can I enable and use Nest shutdown hooks using app.enableShutdownHooks() and creating an ExitAppService service that impements OnModuleDestroy? One thing I am not sure how should I notify it of the desired exit code? Using some kind of cache storage (or even using Redis)? 🤔

Anyway, I have just found that we can displaying an error in commander, e.g. program.error('Custom processing has failed', { exitCode: 2, code: 'my.custom.error' }). Is there a way to do this in Nest Commander too?

[jmcdo29]

Yeah, you can access the commander instance (program in the above line) via @InjectCommander() and then use this.commander.error('Error message', options)

[jmcdo29]

As for the shutdown hooks, it's technically now possible to enable those using the CommandFactory.createWithoutRunning() that I mentioned in your other question today.

[tukusejssirs]

I don’t think that I should use shutdown hooks in this case, as I think commander does the error outputting and exit code usage quite good. Still I think it might be a nice addition to Nest Commander to collect all the error codes and list them in the help. For now, I need to do this manually.

Anyway, do you re-export Command from commander? I could not find it, therefore I need to export it under a different name directly from commander.

import {Command as cmd} from 'commander'

constructor(@InjectCommander() private readonly commander: cmd) {
  super()
}

[jmcdo29]

Currently, no, it is not exported from nest-commander. I should look into doing that though

[tukusejssirs]

Yeah, I think it might be a good idea, however, we can always fall back to importing it from commander. 🤷‍♂️