Optimize class properties output

[Andarist]

Q	A
Fixed Issues?	n/a
Patch: Bug Fix?	no
Major: Breaking Change?	no
Minor: New Feature?	no
Tests Added + Pass?	Yes
Documentation PR	no
Any Dependency Changes?	no

Similar to change in #6652 . Additionally I switch to using defineProperty helper instead of using bare Object.defineProperty call - which should have benefit of not having to hit slow Object.defineProperty path in most cases.

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/7606/

[nicolo-ribaudo]

Using the defineProperty helper looks good, but I don't really like the nested defineProperty calls.

_defineProperty(_defineProperty(this, "foo", 1), "bar", 2);

_defineProperty(this, "foo", 1);
_defineProperty(this, "bar", 2);

The second is objectively longer after minification (4 bytes), but I think it is much easier to read.

[Andarist]

The second is objectively longer after minification (4 bytes), but I think it is much easier to read.

That is a valid concern, was thinking about it too, but ain't sure if we should optimize compiled output for readability.

I've implemented this defineProperty calls folding as little experiment, because I've noticed it's easier for a minifier (at least UglifyJS) to detect single call's result as unused. Assignments to objects (static properties in this case) and calling functions (defineProperty here) with that object effectively prevent dead code elimination of the class in most cases - that's also probably true when considering imperfect algorithm for dead code elimination, but we could do a little bit to help it here.

[existentialism]

Sorry for delay in review, 👍.

FWIW, I don't have a terribly strong opinion re: folding vs readability, but I tend to favor not optimizing for readability.