How to do a regex negative lookahead in a ee.String.replace()?

Question

I thought this would work, but it doesn't:
var someText = ee.String("1_2_text").replace('(?:d_)*(?!d)','').aside(print)

I would expect 1_2_ to be matched and replaced with nothing. Instead I am getting the following error:
String (Error)
String.replace: Invalid regular expression: '(?:d_)*(?!d)' (invalid perl operator: (?!).

which is very confusing, since I don't even use Perl. I guess Earth Engine uses Perl behind the scenes, even though this isn't documented anywhere, but anyway, Perl supports negative lookaheads.

Noel Gorelick · Accepted Answer

It's not exactly Perl, it's that the lookahead operator you're trying to use is part of an extended regex expression language commonly referred to as PERL-re.  Earth Engine uses RE2 instead (in which that operator isn't supported).
If you're just looking to match and replace any leading numeric+underscore prefixes, I think this should get you there:
.replace('^([0-9]+_)*', '')

How to do a regex negative lookahead in a ee.String.replace()?

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