LOWERCASE_EVENT_ATTRIBUTE
A function was set on a lowercase on* (or on:) attribute, which is not an event handler in 2.0; use onXxx (dev; client).
What you saw
- Kind:
render - Severity:
warn(code that works but is structurally wrong or expensive)
The console report opens with [LOWERCASE_EVENT_ATTRIBUTE] and the message, then an in line naming the owners that enclose the subject, root first, and an at line with the source location when the code was compiled with one.
In a captured artifact the same finding is an event with code: "LOWERCASE_EVENT_ATTRIBUTE", ownerPath, and loc.
Diagnostics explains each line.
Why it fires
A function was set on an attribute whose name starts with on but is not an event handler (data.name): a lowercase onclick, or a leftover 1.x on:click.
In 2.0 only on + an uppercase letter binds an event; anything else is a plain attribute, so the function was stringified into it and never runs.
Once per attribute name.
The server runtime reports on the same channel, with the same in <App> › <Page> line.
Two groups.
Findings (SSR_RENDER_ERROR_CONTAINED, SSR_SUBTREE_ABANDONED, SSR_STREAM_ABANDONED, LATE_HEADER_WRITE, DYNAMIC_ASYNC_COMPONENT, SERVER_ERROR_SANITIZED, FRAME_MARKER_CORRUPTED) are facts about a render that exist in observe builds too — an APM sees them in production; in dev they print.
Checks (the rest, SSR_BOUNDARY_WATERFALL and SSR_CLIENT_CONTENT_MASKED included) are dev-only guidance.
A captured artifact from a server render carries both.
How to fix it
Fix: use the camelCase handler (data.handler — onclick={save} → onClick={save}); keep a lowercase name only for a string inline-handler attribute.
In tests
captureArtifact from @solidjs/diagnostics runs a scenario with the diagnostics channel open and returns the events it saw.
expectNoDiagnostics(artifact) fails while LOWERCASE_EVENT_ATTRIBUTE is among them, with the events as evidence; after the fix, the code is gone from artifact.diagnostics.
Check for regressions in tests shows the loop and the Vitest matcher form.
Learn more
- Diagnostics: every code, with its kind, severity, and trigger.
- Debugging reactivity: how to read a report and what each group of codes points at.