Shopify Polaris Web Components Event Values are `undefined`

Summary

Shopify Polaris web components' events (onChange, onInput, etc.) fire correctly but always return undefined values when accessed through event.target.value or event.currentTarget.value inside WXT content scripts, regardless of whether using vanilla JavaScript or Preact.

Test Scenarios Demonstrated

The demo includes 4 comparison scenarios:

Key Observations

1. Events fire correctly: The event handlers are triggered properly in both vanilla JS and Preact
2. Values are undefined in both: event.target.value returns undefined for Polaris components regardless of whether using vanilla JS or Preact
3. Framework-agnostic issue: The problem affects Polaris components even with vanilla JavaScript, not just Preact
4. Regular elements work: Plain HTML elements and Shadow DOM elements work fine
5. Works outside WXT: Same code works in regular apps (CodeSandbox)

Reproduction

https://github.com/junaidkbr/wxt-preact-polaris

Steps to reproduce

No response

System Info

System:
  OS: macOS 15.6.1
  CPU: (12) arm64 Apple M2 Max
  Memory: 2.34 GB / 32.00 GB
  Shell: 5.9 - /bin/zsh
Binaries:
  Node: 22.13.0 - ~/.nvm/versions/node/v22.13.0/bin/node
  Yarn: 1.22.22 - ~/.nvm/versions/node/v22.13.0/bin/yarn
  npm: 11.1.0 - ~/.nvm/versions/node/v22.13.0/bin/npm
  bun: 1.2.15 - ~/.bun/bin/bun
Browsers:
  Chrome: 140.0.7339.133
  Edge: 114.0.1823.67
  Safari: 18.6
npmPackages:
  preact: ^10.26.9 => 10.26.9
  wxt: ^0.20.6 => 0.20.7

Used Package Manager

bun

Validations

• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
• The provided reproduction is a minimal reproducible example of the bug.

Start with the linked minimal reproduction and inspect how WXT content scripts receive Polaris events, comparing event.target.value and event.currentTarget.value with the plain HTML and Shadow DOM scenarios. Done means the Polaris event values are accessible in vanilla JavaScript and Preact content scripts, with the reproduction demonstrating the corrected behavior.