Support optional private prop?

[fisker]

class A{a(){obj?.#x.a}}

[3cp]

How did you access a private prop from outside of class definition of obj?

> class B {
... #p = 2;
... foo() { return this.#p; }
... }
undefined
> var b = new B;
undefined
> b.foo()
2
> b.#p
... ;
b.#p
 ^

Uncaught SyntaxError: Private field '#p' must be declared in an enclosing class
> b['#p']
undefined

[fisker]

class A{
	#x = {a: 1}

	a(){
		return this?.#x.a
	}
}

new A().a()

[fisker]

class A{
	#x = {a: 1}

	a(){
        const obj = this
        return obj?.#x.a
	}
}

new A().a()

[fisker]

How did you access a private prop from outside of class definition of obj?

Not outside, inside.

[3cp]

obj?.#x means obj ? obj.#x : undefined. So it doesn't make much sense here because this is never undefined.

It probably makes sense for obj.#y?.a, but again it does not really make sense, because private prop is statically checked by js compiler.

> class A{
...   #x = {a: 1}
... 
...   a(){
...         const obj = this
...         return obj.#y.a
...   }
... }
... ;
        return obj.#y.a
                  ^

Uncaught SyntaxError: Private field '#y' must be declared in an enclosing class

One possible usage might be

class A {
  #x; // undefined
  a() {
    return this.#x?.a;
  }
}

And yes, this code is fine in meriyah.

My argument is because private prop is statically checked, it doesn't make any sense to have any?.#private syntax. I will be surprised if ecma allows this. @KFlash any thought?

[KFlash]

Just follow what the proposal says

[fisker]

You point make sense, I wounder why Private Fields in in? Seems static check fails on superClass privete field too

class A{
	#x = {a: 1}
}
class B extends A{
	a(){
        return this?.#x.a
	}
}

new B().a()
Uncaught SyntaxError: Private field '#x' must be declared in an enclosing class

[fisker]

This?

class A {
#a=1
a() {return this?.#a}
}

A.prototype.a.call(undefined)
A.prototype.a.call(new A)

[3cp]

Private class fields and methods

Issue #28: Should optional chains support the upcoming private class fields and private methods, as in a?.#b, a?.#b() or a?.b.#c? Quoting microsoft/TypeScript#30167 (comment):

This one isn't baked into the proposal yet, simply because private fields themselves aren't baked yet. So we don't want to hold up this proposal if that one happens to stall out. Once that one has reached Stage 4, we will address it then.

tc39/proposal-optional-chaining#28
tc39/proposal-class-fields#301
tc39/proposal-class-fields#302

[3cp]

In short, there were lots of arguments like ours. But it's in the proposal now.