Rule proposal: Require declaring class members upfront

Declaring the members upfront as class fields makes code more readable and can prevent typos. We would also allow initializing in the constructor, but I think we should auto-fix to class field as it’s neater.

Inspired by https://github.com/eslint/eslint/issues/11540.

Any suggestions on the rule name?

Fail

class X {
	func setName(name) {
		this.name = name;
	}

	func say() {
		console.log(this.name);
	}
}

Pass

class X {
	name;

	func setName(name) {
		this.name = name;
	}

	func say() {
		console.log(this.name);
	}
}

---

How it would prevent typos:

class X {
	name;

	func setName(name) {
		this.name = name;
	}

	func say() {
		// This would have resulted in `undefined` being printed without this rule.
		console.log(this.myName); // ESLint error
	}
}

[fisker]

Yes, it’s clear, let’s add this rule.

I’ll add proposal about the member order later, on vacation.

[sindresorhus]

Your proposal title “Require declaring class members upfront”, didn’t you mean properties should come before the methods? So I proposed a more general rule.

Ah, no. Sorry for being unclear. It’s more like no-undef. By “upfront”, I meant that the members must be declared before being used.