Thank you for these additions!

#2: Using an object here is a good idea, but this approach will become redundant if you have multiple keys for one value. In PHP8 you can comma-separate keys:

$fontWeight = match ($weight) {
  100, 200 => "Super Thin",
  300 => "Thin",
  400, 500 => "Normal",
  600, 700, 800 => "Bold",
  900 => "Heavy",
  default => "Not valid"
};

Also you can directly set a default value.

#3: It’s now even part of ES2020, so no need for the babel plugin anymore.