Fix Bootstrap JavaScript jQuery 4 compatibility on Drupal ~11.3 (core ships jQuery 4)

Problem/Motivation

Drupal ~11.3 core ships jQuery 4. The bundled Bootstrap 4 JavaScript in js/bootstrap/bootstrap.min.js has a version gate that rejects jQuery 4 and throws: Bootstrap's JavaScript requires at least jQuery v1.9.1 but less than v4.0.0. When it throws, the front end breaks: sticky header, scroll classes, dropdowns, collapse/navbar toggler, modal, carousel.

Steps to reproduce

Install the theme as default on Drupal ~11.3 and open any front-end page; the browser console shows the jQuery version error and Bootstrap behaviours do not run.

Proposed resolution

Patch the bundled Bootstrap JS jQuery gate from t[0]>=4 to t[0]>=5 so Bootstrap 4.6 runs on core jQuery 4. Same approach used by the bootstrap4 theme (3.0.7) and the bootstrap theme (8.x-3.35). Add a js/bootstrap/README.md documenting the fix and how custom themes and modules should migrate jQuery 3 code to jQuery 4.

Remaining tasks

• ✅ File an issue about this project
• ✅ Addition/Change/Update/Fix to this project
• ✅ Testing to ensure no regression
• ➖ Automated unit/functional testing coverage
• ➖ Developer Documentation support on feature change/addition
• ➖ User Guide Documentation support on feature change/addition
• ➖ UX/UI designer responsibilities
• ➖ Accessibility and Readability
• ✅ Code review by maintainers
• ✅ Full testing and approval
• ✅ Credit contributors
• ✅ Review with the product owner
• ✅ Update Release Notes
• ✅ Release varbase-9.2.0, vartheme_bs4-9.2.0

User interface changes

• N/A

API changes

• N/A

Data model changes

• N/A

Release notes snippet

• fix: #3607041 Bootstrap JavaScript jQuery 4 compatibility on Drupal ~11

Read more

• Drupal core: [11.x] Update to jQuery 4.0.x (#3411839)
• Bootstrap upstream: jQuery 4 support for Bootstrap 4 (twbs/bootstrap #42023)
• Bootstrap4 theme: jQuery 4 compatibility, fixed in 3.0.7 (#3549897)
• Bootstrap theme: jQuery 4 compatibility, 8.x-3.35 (#3464373)
• Radix theme: jQuery 4 error and workarounds (#3530127)
• jQuery Core 4.0 Upgrade Guide