Chat input (typing-time feedback)

The user types into a chat composer. The input must echo inside the perceptual frame Card-Moran-Newell Card, Moran & Newell 1983 describe — anything the input does that blocks for more than 50 ms (typeahead suggestions, mention parsing, markdown preview) puts the user in the same active-mode trap search-as-you-type covers.

The reuse-affinity is high: a chat composer is a search input plus a send button. Eizenberg's Eizenberg production-surface argument is the same here — every perception trick must protect the input itself, not paper over it.

What is happening

Same demo as search-as-you-type, framed for the chat case. Naive: synchronous work on every keystroke blocks the input. Tuned: useDeferredValue keeps the input live while the work happens at low priority. Whether the work is "filter a list" or "render markdown preview" or "parse @mentions," the structural answer is the same.

For the send button itself, pair this with optimistic-actions: on Send, render the user's message in the conversation immediately; stream the assistant response in parallel.

What to tune

1. Keystroke echo — character renders inside ~50 ms. Anything that blocks the input (markdown parse, mention lookup) runs at low priority via useDeferredValue.
2. In-flight side work — markdown preview, mention suggestions, autocomplete all run stale-while-revalidate. The input never waits on them.
3. Send press — pre-action feedback within ~50 ms; the button echoes regardless of how long the message takes to commit.
4. Optimistic commit — render the user's message in the conversation immediately on Send; clear the composer; let the assistant response stream in parallel.
5. Completion — focus returns to the (now-empty) input so the user can keep typing.

When perceived performance hurts you here

Composer surfaces are pure production. A skeleton over the textarea, a spinner over the send button, a "thinking" placeholder where the user is typing — all wrong. Miller 1968's Miller 1968 keystroke-echo tier is unforgiving: if the input lags, no perception trick saves it.

Accessibility

1. Don't lose focus on send. After the message commits, focus returns to the (now-empty) input so the user can keep typing.
2. aria-multiline="true" on textareas; let the browser handle line breaks correctly.
3. prefers-reduced-motion for any markdown preview animations.
4. Keyboard send convention — Enter to send, Shift+Enter for newline. Document it visibly the first few times.

References