Allow `#`-private names in parameter property positions

Search Terms

hard privacy https://github.com/microsoft/TypeScript/issues/31670

Suggestion

allow create hard privacy like we do private in constructor(private foo: number)

Use Cases

Examples

allow use constructor(#foo: number) {} or constructor(private #foo: number) {} or constructor(hard private #foo: number) {}

for same as

#foo: number;
constructor(foo: number) {
		// This works.
		this.#foo = foo;
	}

class C {
	constructor(#foo: number) {}

	log() {
		console.dir(this.#foo);
		return this
	}
}

let o = new C(777).log();

// error
o.#foo;

same as

class C {
	#foo: number;

	constructor(foo: number) {
		// This works.
		this.#foo = foo;
	}

	log() {
		console.dir(this.#foo);
		return this
	}
}

let o = new C(777).log();

// error
o.#foo;

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

No files, tests, or entry points are named. Start by reviewing the requested constructor parameter forms and the accompanying class examples; done means supporting the proposed #foo parameter-property syntax while retaining the shown private access behavior.