Use this instead of Command as a return type in TypeScript

[vonagam]

Pull Request

Problem

import { Command } from 'commander';

class CustomCommand extends Command {
  customMethod() {
    return this;
  }
}

const custom = new CustomCommand();

custom
  .description('a custom method will be treated as `any` after that')
  .customMethod(); // no type checks here or after that

Because right now description and other chainable methods return Command and not this, type information of subclasses gets inaccessible after a call to an inherited method (and would have otherwise caused an error if not for [key: string]: any in Command for storing parsed options on a instance).

Solution

Changed return type to this in chainable methods.

Also made parseAsync return Promise<this> instead of returning Promise<_actionResults> to be consistent with parse. (This change is little off topic, can remove if you want to expose _actionResults)

(This PR to develop branch, not master)

[shadowspawn]

My first impressions are favourable. 😃

1. Related Support subclassing Command #1002

2. Could also change return type of command() signature for adding stand-alone executable?

 command(nameAndArgs: string, description: string, opts?: commander.CommandOptions): Command;

3. parseAsync: when I added .parseAsync(), .parse() did not have a well behaved return type and I deliberately did not match it. However, now on the develop branch .parse() is well behaved and I am interested in your change.

[vonagam]

About second point. As you said in the mentioned issue:

That might be doable using a factory method to create the new object, but definitely more complicated than just changing the TypeScript definition for .command

Because if you do not redefine command in subclass, then you should expect Command class and not your subclass, since that what you would get.

import { Command } from 'commander';

class CustomCommand extends Command {
  customMethod() {
    return this;
  }
}

const custom = new CustomCommand();

custom
  .command('subcommand') // this returns Command, not CustomCommand
  .customMethod(); // this is untyped and causes a runtime error

But if you redefine command in subclass to return that subclass, then it will work and typescript allows it.

import { Command } from 'commander';

class CustomCommand extends Command {
  command( ...args: any[] ) {
    const hack = super.command( ...args );
    const command = new CustomCommand();
    Object.assign(command, hack);
    return command; 
  }

  customMethod() {
    return this;
  }
}

const custom = new CustomCommand();

custom
  .command('subcommand') // this is CustomCommand type
  .customMethod(); // this is properly typed and works

[shadowspawn]

I was referring in this PR to the "other" signature for .command() when it is passed a description, and when it does just return this.

const custom = new CustomCommand();

custom
  .command('sub1', 'implemented in stand-alone executable')
  .command('sub2', 'implemented in stand-alone executable')
  .customMethod();

[vonagam]

Ah, sorry, misunderstood.

[shadowspawn]

The two different behaviours of .command() are a great source of confusion, but this change will in a small way make it clearer.

[shadowspawn]

LGTM

[abetomo]

👍

[shadowspawn]

Commander v5.0.0 has been released.

https://github.com/tj/commander.js/releases/tag/v5.0.0