Add hooks for life cycle events: using .hook()

[shadowspawn]

Pull Request

Problem

People ask for a way to run code before the action handler with access to the parsed options. And also some requests for a hook after the action.

Main issue: #1197
Related issues: #76 #229 #936 #996 #1158 #1457

Solution

Add .hook(event, callback) method

• supports async callbacks
• supports multiple hooks for same event on single command

Supported hooks: preAction, postAction. Triggered by action handler for hooked command and its subcommands.

Callback is passed the hooked command and the command running the action handler.

ChangeLog

• add .hook() with support for "preAction" and "postAction" callbacks

[shadowspawn]

Why not preHandler or afterHandler to also cover executable? The stand-alone executable seems quite different, and I have been avoiding tackling! Initial concerns without deep digging:

• the command which is about to be "executed" is a dummy command
• the command object which is about to be executed does not currently have .args set
• the program gets terminated when the subprocess finishes (?), but could perhaps run afterHandler before exit? But what about async?

[shadowspawn]

As noted in #1519 (comment), the .hook() api signature is similar to that used by Fastify:

https://www.fastify.io/docs/latest/Hooks/

[abetomo]

LGTM

[shadowspawn]

Thanks @abetomo

I'll take another look at the code refactor next, and then focus on a prerelease of Commander v8.