Monday, February 18, 2019

is dotAll you got? (frustrations with firefox multiline string matching)

There's growing discontent among developers with Chrome as a browser (and the risk of it becoming a kind of monoculture in the way IE was, albeit not quite as crappily and a bit more standards-compliant) and many are making the leap to Firefox. And recently I was delighted to see that the developer tools were pretty much at parity with Chrome's, and used many of the same UI patterns as well.

But I found Firefox was choking on some regular expressions I put into the backend tooling for my website.
SyntaxError: invalid regular expression flag s
That s flag, letting an expression like /(.*)/s match multiple lines (because it says to treat linebreaks as normal whitespace-ish stuff) was a critical tool going back to my Perl days...

So to quote T.J. Crowser in StackOverflow:
You are looking for the /.../s modifier, also known as the dotall modifier. It forces the dot . to also match newlines, which it does not do by default.
The bad news is that it does not exist in JavaScript (it does as of ES2018, see below). The good news is that you can work around it by using a character class (e.g. \s) and its negation (\S) together, like this:
His examples then show `[\s\S]` replacing good old `.`. I'm happy to have the workaround, but man is that an ugly one!

I wish I knew more about the history here - feels like Firefox was sticking to the spec more righteously than Chrome, which I guess is fair enough, but why was such a critical piece missing from JS/ECMAScript in the first place? It smells a little bit like some religious war fallout, some coders didn't like multiline conceptually, or something...

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