Tslint: Rule suggestion: prefer-parameter-properties

[danvk]

There's a no-parameter-properties rule, but what if you like them? How about a rule that flags code like this:

class Foo {
  foo: number;
  constructor(foo: number) {
    this.foo = foo;
  }
}

in favor of this:

class Foo {
  constructor(public foo: number) {
  }
}

Another option would be to replace no-parameter-properties with a more general parameter-properties rule that lets you say how you feel about them.

See parameter properties in the TS handbook.

[adidahiya]

Sure, that sounds good. I would like it to be one rule though, so let's add parameter-properties with options "always" | "never" and deprecate no-parameter-properties.

[codingthat]

What was the motivation for this rule in the first place, BTW? I only see benefits to the "always" way, so I'm curious. :)

[adidahiya]

@codingthat mostly just consistency with other languages like Java for full-stack developers.

[codingthat]

@adidahiya That being the case, I'm even happier to see the rule go neutral. :)

[adidahiya]

I mean, it _is_ harder to see the list of class members at a glance when you use parameter properties. New language features almost always add more cognitive load.

[codingthat]

Depends on your formatting, maybe :) That's a good point to consider though.

[JoshuaKGoldberg]

FWIW, parameter properties are quite nice when using libraries such as Inversify:

@injectable()
class Ninja implements Warrior {

    private _katana: Weapon;
    private _shuriken: ThrowableWeapon;

    public constructor(
        @inject(TYPES.Weapon) katana: Weapon,
        @inject(TYPES.ThrowableWeapon) shuriken: ThrowableWeapon
    ) {
        this._katana = katana;
        this._shuriken = shuriken;
    }

    public fight() { return this._katana.hit(); };
    public sneak() { return this._shuriken.throw(); };
}

..compared to...

@injectable()
class Ninja implements Warrior {
    public constructor(
        @inject(TYPES.Weapon)
        private readonly katana: Weapon,

        @inject(TYPES.ThrowableWeapon)
        private readonly shuriken: ThrowableWeapon,
    ) {  }

    public fight() { return this.katana.hit(); };
    public sneak() { return this.shuriken.throw(); };
}

[JoshuaKGoldberg]

Note: per #4534, this issue will be closed in less than a month if no PR is sent to add the rule. If you _really_ need the rule, custom rules are always an option and can be maintained outside this repo!

[JoshuaKGoldberg]

💀 _It's time!_ 💀

TSLint is being deprecated and no longer accepting pull requests for new rules. See #4534. 😱

If you'd like to see this rule implemented, you have two choices:

• Recommended: Use typescript-eslint to lint your TypeScript code with ESLint ✅
• Legacy: Write it as a custom TSLint rule 🤷‍♂️

👋 It was a pleasure open sourcing with you!

_If you believe this message was posted here in error, please comment so we can re-open the issue!_