Forms: conditional logic (3/5) — apply in the browser

[enejb]

Part 3 of 5. This series splits #50938 into reviewable pieces. Each PR is based on the previous one, so the diff shown here is incremental.

1. Forms: conditional logic (1/5) — vocabulary and feature flag #50976 — vocabulary and feature flag
2. Forms: conditional logic (2/5) — the resolver, in JS and PHP #50977 — the resolver, in JS and PHP
3. Forms: conditional logic (3/5) — apply in the browser #50978 — apply in the browser
4. Forms: conditional logic (4/5) — server-side render and validation #50979 — server-side render and validation
5. Forms: conditional logic (5/5) — the editor panel #50980 — the editor panel

Proposed changes

Part 3 of 5 splitting #50938. Wires the resolver into the front-end form so fields appear and disappear as the visitor answers, and skips hidden fields when validating.

• Visibility is memoised per form rather than globally. Two forms on one page have their own rules and answers, and a single shared cache let one form's result satisfy the other's lookup.
• Hidden fields use display: none as the base state, so a visitor with JavaScript or animations off still gets a correct form. The reveal animation is purely additive, scoped to conditional fields, and inside @media not (prefers-reduced-motion).

Related product discussion/links

• https://wp.me/p1HpG7-xBk

Does this pull request change what data or activity we track or use?

No.

Testing instructions

The server does not stamp conditional markup until part 4, so the easiest way to exercise this alone is the unit tests:

• jetpack test js packages/forms — conditional-visibility.test.js covers the cascade, the per-form isolation, and the hidden-field validation skip.

For a live check, enable the flag and use a form whose fields already carry data-jp-conditional (or wait for part 4, which emits it):

• Type into the field a rule depends on and confirm the dependent field appears/disappears immediately.
• Confirm a hidden required field does not block submission.
• With "Reduce motion" enabled in the OS, confirm the field still appears — just without the transition.

[github-actions]

Are you an Automattician? Please test your changes on all WordPress.com environments to help mitigate accidental explosions.

• To test on WoA, go to the Plugins menu on a WoA dev site. Click on the "Upload" button and follow the upgrade flow to be able to upload, install, and activate the Jetpack Beta plugin. Once the plugin is active, go to Jetpack > Jetpack Beta, select your plugin (Jetpack), and enable the add/forms-conditional-logic-frontend branch.
• To test on Simple, run the following command on your sandbox:

bin/jetpack-downloader test jetpack add/forms-conditional-logic-frontend

Interested in more tips and information?

• In your local development environment, use the jetpack rsync command to sync your changes to a WoA dev blog.
• Read more about our development workflow here: PCYsg-eg0-p2
• Figure out when your changes will be shipped to customers here: PCYsg-eg5-p2

[github-actions]

Thank you for your PR!

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[jp-launch-control]

Code Coverage Summary

No summary data is available for parent commit 0cc8354, so cannot calculate coverage changes. 😴

If that commit is a feature branch rather than a trunk commit, this is expected. Otherwise, this should be updated once coverage for 0cc8354 is available.

Full summary · PHP report · JS report