Bug 174931 - Implement RegExp lookbehind assertions
Summary: Implement RegExp lookbehind assertions
Status: ASSIGNED
Alias: None
Product: WebKit
Classification: Unclassified
Component: JavaScriptCore (show other bugs)
Version: WebKit Nightly Build
Hardware: Unspecified Unspecified
: P2 Enhancement
Assignee: Michael Saboff
URL: https://github.com/tc39/proposal-rege...
Keywords: InRadar
: 226465 (view as bug list)
Depends on:
Blocks:
 
Reported: 2017-07-28 00:44 PDT by Mathias Bynens
Modified: 2022-09-23 12:02 PDT (History)
55 users (show)

See Also:


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Description Mathias Bynens 2017-07-28 00:44:39 PDT
https://github.com/tc39/proposal-regexp-lookbehind
Comment 1 Radar WebKit Bug Importer 2017-07-29 11:45:21 PDT
<rdar://problem/33608833>
Comment 2 Michael Saboff 2017-07-31 15:10:29 PDT
<rdar://problem/33183185>
Comment 3 Masataka Yakura 2020-04-10 09:22:20 PDT
it looks like devs started to use it in the wild without fallback :(

steamcommunity.com - Page doesn't load after signing into Steam account · Issue #51385 · webcompat/web-bugs
https://github.com/webcompat/web-bugs/issues/51385
Comment 4 md331 2020-06-04 06:50:02 PDT
ES2018 regex has landed in the beta channel of FF (https://bugzilla.mozilla.org/show_bug.cgi?id=1225665) due out end of June 2020. That'll mean Chrome, Edge, and FF support it but Safari still does not.
Comment 5 Tobias Uhlig 2021-06-19 14:01:49 PDT
I actually used it for a neo.mjs viewmodel regex and just got a heads up that dist/prod builds no longer work in safari due to this =/

Well, at first I got a report "breaks on mobile" => did not get a JS error inside my remote debugging tools, but luckily it is reproducable on desktop.

Adding this feature would be highly appreciated!

Thanks,
Tobias
Comment 6 James Livesey 2021-06-20 05:44:22 PDT
As somebody who uses lookbehind in regex for a lot of my code, I would like to show my strong support for the resolution of this issue. Considering that all modern browsers -- save for Safari/WebKit -- support regex lookbehind, as a web developer, I find it frustrating that WebKit is the only modern browser engine which does not support this.

Which, at the moment, means that I unfortunately must resort to excluding those who use Safari/WebKit browsers from accessing some of my projects, and by extension, those who use iOS/iPadOS devices too (since the use of WebKit in any web browser is unfortunately mandatory).

From the report date, this issue has been around since 2017, so it is coming up to the 4-year anniversary of this issue existing, as of the time of writing. I hope that by giving my remarks on this issue, the WebKit developers take notice and implement this feature which really should have been added in some time ago.

According to earlier comments, it seems that many major platforms have used regex lookbehind, which completely renders sites unusable for iOS users. Though I am not an iOS, iPadOS or macOS user myself (in part because of my views on Apple's App Store browser engine policy), I would like to see this change so that iOS/iPadOS users in particular can enjoy not just my services, but others' services too.

If this issue is being worked on as we speak, I would like to therefore thank the WebKit developers in doing so.
Comment 7 Alexey Shvayka 2021-07-23 16:58:45 PDT
*** Bug 226465 has been marked as a duplicate of this bug. ***
Comment 8 Marvin 2021-07-29 00:17:58 PDT
Can this be given a higher priority? All major browser except Safari support it and it has been opened for four years now...

I want to use negative lookbehinds in our Ionic app which uses WKWebView. This would really reduce some complicated Regex.
Comment 9 Simon Lampen 2021-08-18 19:58:26 PDT
Yes I agree, it would be great if be brought inline with all the other current evergreen browsers and also to the up coming spec too.
Comment 10 VLang 2021-08-31 02:39:00 PDT
I've been tracking this one for years and I'm finally throwing a comment in here in the hope it gets bumped in priority.

Due to the fact that Apple products force all browsers to use JavaScriptCore, this means that Lookbehinds still won't wont work on *most* browsers in the United States. It actually means that less Americans can use apps with Lookbehinds than can people in countries with lower GDPs (due to Apple products being more expensive)!
Comment 11 VLang 2021-09-04 14:58:59 PDT
To anyone tracking this, I emailed the Assignee of this bug and he said "We plan on getting to it in the next couple of months."

Fingers crossed
Comment 12 James Livesey 2021-09-05 04:52:30 PDT
Brilliant news if that's the case! Certainly keeping my fingers crossed. It'll be great to hear an ETA for when this will be released -- I personally do not know the time it takes to implement such a feature, but I doubt it should take too long imo. That's just my naïve estimation though!
Comment 13 Nickolay 2021-10-26 07:45:29 PDT
OMG, just stumbled upon this, totally surprised its not supported in Safari (which is supposed to be a "good" browser). Please implement this feature.
Comment 14 Regex Guy 2021-11-09 14:41:35 PST
I really need this feature too :)
Comment 15 Joel Bruner 2021-11-26 16:45:45 PST
+1 to supporting an ES2018 feature in 2022.
WebKit would be a good netizen to do this. 

Here's the relevant assertions in the ES2018 spec:
https://tc39.es/ecma262/multipage/text-processing.html#sec-assertion

Assertion :: ( ? <= Disjunction )
Assertion :: ( ? <! Disjunction )

For casual computing laymen like me :)
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions/Assertions#other_assertions

(?<=y)x	
Lookbehind assertion: Matches "x" only if "x" is preceded by "y".

(?<!y)x	
Negative lookbehind assertion: Matches "x" only if "x" is not preceded by "y".


I like this optimistic summary with it's "done and dusted" attitude, with only a caveat for "older browsers" (and I think WebKit would NOT like being lumped in with IE!)

https://www.regular-expressions.info/javascript.html

> Lookbehind was a major omission in JavaScript’s regex syntax for the longest time. Lookbehind is part of the ECMAScript 2018 specification. It is supported by the latest versions of Chrome, Edge, and Firefox but not by older browsers such as Internet Explorer.

It would be nice for it to be correctly assumed that webkit/jsc supports an ES2018 feature in 2022. Thanks! :D
Comment 16 Regex Guy 2022-03-14 23:36:19 PDT
Will we get this before Climate Collapse?
Comment 17 Steve Nicolai 2022-04-08 17:14:59 PDT
I've hit a website in the wild that uses lookbehind assertions and does not load on Safari.

https://russiaslosses.netlify.app
Comment 18 SCWR 2022-04-18 20:11:43 PDT
(In reply to VLang from comment #11)
> To anyone tracking this, I emailed the Assignee of this bug and he said "We
> plan on getting to it in the next couple of months."
> 
> Fingers crossed

Is there a latest news?
Comment 19 moo1210 2022-04-23 00:46:47 PDT
We just noticed some of the code for our extension doesn't work because of this. This badly needs to be supported, it is a standard in all other browsers.
Comment 20 Orlin 2022-05-18 23:36:43 PDT
Extremely important so that our app works in both the Safari browser and with the WKWebview on iOS. Please implement asap. Thank you in advance.
Comment 21 Jared Hobbs 2022-05-25 14:53:43 PDT
just hit this bug trying to load a local instance of backstage (https://github.com/backstage/backstage)

following.
Comment 22 Joao Brito 2022-06-22 02:46:02 PDT
I'm having the Same Problem.

Any new feedback on the solution for Safira Browser?
Comment 23 James Livesey 2022-06-22 02:54:27 PDT
Not really any new feedback as of yet; there's not really an easy workaround to this issue in JavaScript, either (without having to essentially write your own parser), but this does depend on what your JS code is actually doing.

There hasn't been much progress on this issue for... *checks date* almost 5 years... I feel like I should send out some invitations for this issue's 5th birthday party on the 28th of July! Who's coming‽

In all seriousness, this has been a feature in Chrome since 17 October 2017, and in Firefox since 30 June 2020. Safari is still yet the only major browser to not implement this feature.

WebKit, we'd love it if you would take up this issue and start working on it ─ thanks!
Comment 24 VLang 2022-06-23 23:48:11 PDT
(In reply to James Livesey from comment #23)
> Not really any new feedback as of yet; there's not really an easy workaround
> to this issue in JavaScript, either (without having to essentially write
> your own parser), but this does depend on what your JS code is actually
> doing.
> 
> There hasn't been much progress on this issue for... *checks date* almost 5
> years... I feel like I should send out some invitations for this issue's 5th
> birthday party on the 28th of July! Who's coming‽
> 
> In all seriousness, this has been a feature in Chrome since 17 October 2017,
> and in Firefox since 30 June 2020. Safari is still yet the only major
> browser to not implement this feature.
> 
> WebKit, we'd love it if you would take up this issue and start working on it
> ─ thanks!

Hell yeah! Flooding this one with comments next month. T minus 24 days!
Comment 25 VLang 2022-06-23 23:49:49 PDT
Correction, 34 days. Same diff, 5 years.
Comment 26 Simon Chang 2022-07-05 17:15:51 PDT
So long. So much needed. So prevailing in usages. So unavoidable. It’s just incredibly puzzled why a modern browser still lacks this feature especially they’ve supported regexp lookahead. Sadly I’m iOS from WKWebview and Safari users have no option to choose alternatives to open pages using this. Puzzled. Will we get this implementation this year?
Comment 27 Simon Chang 2022-07-05 17:27:10 PDT
(In reply to Regex Guy from comment #16)
> Will we get this before Climate Collapse?

And this shines.
Comment 28 zack 2022-07-22 14:21:42 PDT
just when you thought you had the right regex
Comment 29 Míng 2022-07-27 03:15:48 PDT
???: 5 years
Comment 30 Jozef 2022-07-30 04:19:38 PDT
this is sad
Comment 31 Regex Guy 2022-07-31 23:59:09 PDT
"Sad!" - Trump
Comment 32 Sahin Deniz 2022-08-14 05:23:30 PDT
Hi Michael Saboff, do you have any updates regarding the implementation of `lookbehind` and `lookahead` features?
Comment 33 digitalgopnik 2022-09-01 00:54:02 PDT
+1 for higher priority! Fingers crossed, prayed to god, allah, buddha and hanuman! Maybe it'll help!
Comment 34 Orlin 2022-09-02 03:03:49 PDT
Can't wait for this to be fixed, so that our app is full-featured on iPhone.
Comment 35 Simon Chang 2022-09-19 12:52:43 PDT
Can we simply bury this bug after Queen Elizabeth's funeral?
Comment 36 Playtime 2022-09-19 23:04:09 PDT
Just realized our website was broken for weeks on Safari because of this bug! Even more frustrating is that w3school says it was implemented in Safari 12 in September 2018 (https://www.w3schools.com/js/js_2018.asp) ... but apparently not?? Now I know to never assume something works even if websites say it's ok. ALWAYS test!!!

There are probably many other websites out there broken because of this oversight, given that it's from the 2018 standard. Is there any update on this?
Comment 37 Ali Allouch 2022-09-21 22:01:42 PDT
We just realized that our website was broken on safari after 5 months of launching the website on production, and after debugging, we figure out that the problem was a lookbehind RegExp... When will you fix this bug?!
Comment 38 Adam S. 2022-09-23 01:02:33 PDT
Negative lookahead seems to be bugged too.
We use the following regex to search like 100 different HTML texts for different patterns, but skip HTML links. 

\b(?!(?:(?!<\/?[ha].*?>).)*<\/[ha].*?>)(?![^<>]*>)(PATTERN)\b(?!(?:(?!<\/?[ha].*?>).)*<\/[ha].*?>)(?![^<>]*>)

Edge, Safari, Chrome are finishing in under half a second.
Safari takes at least 2 minutes.
Comment 39 Andrei 2022-09-23 03:21:49 PDT
Many sites are broken. When do you plan to add this feature? We must mark last Safari browser as outdated and disable our sites for Safari because you can't implement this simple feature in 5 years. Use Blink on MacOS (iOs) if you don't want to update WebKit.
Comment 40 Regex Guy 2022-09-23 04:08:08 PDT
Safari is officially an outdated browser because of this
Comment 41 Sky 2022-09-23 11:44:22 PDT
I've made an account just to comment on this specific error, which *very* far downstream is still causing problems, even outside of the Safari scope. Please fix this!
Comment 42 Andrei 2022-09-23 12:02:04 PDT
Apple forces to use WebKit for all browsers in App Store. Chrome has implemented this feature a few years ago in their Blink engine, but Chrome Mobile can't use Lookbehind, because it should use WebKit.