Hi,
About the bad old nonstandard RegExp functionalities:
* `RegExp.prototype.compile()` — currently in Annex B;
* `RegExp.$1`, `RegExp.leftContext`, etc. — currently unspecced.
Although we could probably not get rid of them for plain regexps, I think it is
a good idea to disable them for proper subclasses of RegExp (e.g., `class
MyRegExp extends RegExp {}`).
Basically, the reason is that these methods break encapsulation (they operate
on the raw regexp), leading to potential bugs when using them. Moreover
`RegExp.$1` and friends have the additional troublesome property of relying on
a global state that could be unexpectedly modified. For concrete examples of
what could go wrong, see the subclass-restriction-motivation.md subpage in the
proposal linked below.
Here is a link to a possible specification for the regexp statics (RegExp.$1,
...), that includes the disabling of bad legacy features for proper subclasses
of RegExp (and for some edge-cases around cross-realm interactions):
https://github.com/claudepache/es-regexp-legacy-static-properties
<https://github.com/claudepache/es-regexp-legacy-static-properties>
What do you think? Are implementations willing to try?
—Claude
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