Re: Some regular-expression performance hacking

On Thu, Feb 18, 2021, at 19:53, Tom Lane wrote:

>(Having said that, I can't help noticing that a very large fraction

>of those usages look like, eg, "[\w\W]".  It seems to me that that's

>a very expensive and unwieldy way to spell ".".  Am I missing

>something about what that does in Javascript?)

This popular regex

    ^(?:\s*(<[\w\W]+>)[^>]*|#([\w-]+))$

is coming from jQuery:

// A simple way to check for HTML strings

// Prioritize #id over <tag> to avoid XSS via location.hash (#9521)

// Strict HTML recognition (#11290: must start with <)

// Shortcut simple #id case for speed

rquickExpr = /^(?:\s*(<[\w\W]+>)[^>]*|#([\w-]+))$/,

From: https://code.jquery.com/jquery-3.5.1.js

I think this is a non-POSIX hack to match any character, including newlines,

which are not included unless the "s" flag is set.

Javascript test:

"foo\nbar".match(/(.+)/)[1];

"foo"

"foo\nbar".match(/(.+)/s)[1];

"foo

bar"

"foo\nbar".match(/([\w\W]+)/)[1];

"foo

bar"

/Joel