dotnet/aspnetcore

[Blazor] InputText binding is not supported well with Shadow DOM elements

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#60,885 opened on Mar 11, 2025

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area-blazorbughelp wanted

Description

Is there an existing issue for this?

  • I have searched the existing issues

Describe the bug

I use a web component library which create input elements within shadow DOM (shadowRoot property). Let's call it <super-input> I overrided InputText content with .

When using @bind on the value with oninput event, it doesn't work as well as the InputText or html input element. Characters could be sent weirdly depending the connection, and the use or websocket or no, and specially when the typing is fast.

I already digged into the problem and found a fix on my branch : https://github.com/Poppyto/aspnetcore/tree/poppyto/use-shadow-input-with-binding

The idea is to relay on event.composedPath().find(_=>true) instead of event.target when dealing with some events.

I would be happy to discuss about this bug

Expected Behavior

The typing must be smooth

Steps To Reproduce

No response

Exceptions (if any)

No response

.NET Version

8

Anything else?

No response

Contributor guide

Tech stack
csharp
Domain
frontend
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Basic Blazor knowledgeShadow DOM conceptsEvent propagation understanding
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50
Research direction
The issue proposes a fix using event.composedPath() instead of event.target for Shadow DOM elements. A reference branch exists at https://github.com/Poppyto/aspnetcore/tree/poppyto/use shadow input with binding. Investigate the Blazor input binding mechanism in aspnetcore, likely in files related to event handling (e.g., WebEvent.cs or InputText.cs). Review the proposed changes, test with the provided scenario, and ensure no regressions in standard input binding.