Add override to allow throw instead of process.exit

[shadowspawn]

Pull Request

Problem

Commander has multiple calls to process.exit which is hard to override to use as a library and parse multiple strings, as parsing errors or --help terminate the process. Doing a throw instead would allow appropriate handling and carry on.

Issues: #945 #575 #934

Solution

Add .exitOverride(callback) routine to do custom handling of code that would otherwise call process.exit(). The callback is optional and the default behaviour is to throw an instance of CommanderError which includes the exitCode, a string code, and a message.

This allows writing code like:

const program = new commander.Command();
program
  .exitOverride()
  .option(-p, --pepper <type>, 'add pepper');

try {
  program.parse(['node', 'test', '--pepper']);
} catch (err) {
  // custom processing
}

(The routine name exitOverride is a bit implementation specific rather than friendly, but this is an optional feature and not sure how much or how it will be used.)

Limitations

• code flow is not changed, so override still expected to throw or exit and not fall through
• executable subcommand calls spawn as async, not currently overriding those process.exit as different pattern required
• writing to stdout and stderr as normal before override

ToDo

• TypeScript
• README
• not doing tests here as have extensive tests in feature/jest branch

Making the code visible for discussion and review.

[shadowspawn]

One of the prompts for adding this feature was to simplify writing unit tests. The test file for exitOverride itself (on a different branch) is:

https://github.com/shadowspawn/commander.js/blob/feature/jest/tests-jest/command.exitOverride.test.js

[abetomo]

LGTM!

[shadowspawn]

Thanks @abetomo 😄

[shadowspawn]

Added support for async calls in executableSubcommand.

[shadowspawn]

Allows custom exit codes: #188 #436

[shadowspawn]

The implementation already landed in the Jest PR. This PR now effectively promotes it from private _exitOverride to public exitOverride.

Added description to README.

Suggested line for CHANGELOG:

• .exitOverride() allows override of calls to process.exit for additional error handling and to keep program running ([Add override to allow throw instead of process.exit #1040])

[lxsmnsyc]

Hello, I was looking for a solution to prevent "--help" from exiting the CLI.

I tried using exitOverride, but it doesn't really prevent it from exiting. Is there any way for this?

[shadowspawn]

@lxsmnsyc
exitOverride would be my suggestion. Open a new issue with some more details. (I am not sure what you mean by "doesn't really prevent it from exiting".)

[lxsmnsyc]

@lxsmnsyc
exitOverride would be my suggestion. Open a new issue with some more details. (I am not sure what you mean by "doesn't really prevent it from exiting".)

I have found a work around to my problem.

I have to take a look at commander's index js to know how it executes commands, and to understand the behavior in general :)