fix(helpers): ignore wrapper characters in fromRegExp

[ST-DDT]

Fixes #3663

• How to remove built-in regex characters in the output of "fromRegExp" #3663

---

Ignore the anchor characters at the start and end of regex patterns.

faker.helpers.fromRegExp(/^foo$/)
// old: ^foo$
// new: foo

[netlify]

✅ Deploy Preview for fakerjs ready!

Name	Link
🔨 Latest commit	7ab4883
🔍 Latest deploy log	https://app.netlify.com/projects/fakerjs/deploys/69e530f0d0ca4300085de70a
😎 Deploy Preview	https://deploy-preview-3795.fakerjs.dev
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify project configuration.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.90%. Comparing base (c53c1fe) to head (7ab4883).
⚠️ Report is 3 commits behind head on next.

Additional details and impacted files

@@            Coverage Diff             @@
##             next    #3795      +/-   ##
==========================================
- Coverage   98.90%   98.90%   -0.01%     
==========================================
  Files         897      897              
  Lines        3103     3102       -1     
  Branches      556      571      +15     
==========================================
- Hits         3069     3068       -1     
  Misses         30       30              
  Partials        4        4              

Files with missing lines	Coverage Δ
src/modules/helpers/index.ts	95.27% <100.00%> (-0.02%)	⬇️

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[Copilot]

Pull request overview

This PR updates faker.helpers.fromRegExp to ignore start/end anchor characters (^ and $) when a RegExp object is provided, so anchored patterns don’t leak wrapper characters into the generated output (fixes #3663).

Changes:

• Strip ^ / $ anchors from the extracted pattern when fromRegExp receives a RegExp.
• Add a unit test asserting anchored /^foo$/i produces foo.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/modules/helpers/index.ts	Adjusts the RegExp-to-pattern extraction to drop leading/trailing anchors.
test/modules/helpers.spec.ts	Adds coverage for anchored input being unwrapped before generation.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[matthewmayer]

this is arguably breaking, although seems doubtful anyone was relying on this?

[ST-DDT]

The method basically only implements a third of all regex features. So we could declare this as wont't fix, but ^$ are common regex wrappers IMO..

Once the standalone module functions PR is merged, then I'll consider adding a faker-plugins-string-regexp2factory or similar package, that properly parses the regex into an AST (using a lib) in order to generate the output.

[hiSandog]

The regex /\/\^?(.+?)\$?\/ correctly strips optional ^ and '$' anchors from the RegExp string representation.

One edge case to consider: if someone passes /^^foo$$/ (multiple anchors, which is valid regex but redundant), the current pattern would produce ^foo$ since ^? and $? only match zero or one occurrence. This is unlikely in practice, but using ^\^* and \$* (zero or more) would be more robust:

pattern = /\/\^*(.+?)\$*\//.exec(pattern)?.[1] ?? '';

Given that fromRegExp only implements a subset of regex features (as noted in the discussion above), the current fix is pragmatic for the common /^foo$/ case.

[ST-DDT]

@faker-js/maintainers Thoughts?

[Shinigami92]

@faker-js/maintainers Thoughts?

LGTM, this is a bug fix, not a breaking change - nobody should be relying on literal ^/$ leaking into the output.

suggestion: consider using pattern.source instead of parsing toString(), it gives you the pattern without slashes/flags directly:

if (pattern instanceof RegExp) {
  isCaseInsensitive = pattern.flags.includes('i');
  pattern = pattern.source.replace(/^\^/, '').replace(/\$$/, '');
}

a bit more readable and avoids the slash-parsing regex entirely.
Either way, happy to approve.