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hkuds--deeptutor/web/lib/use-auto-sized-textarea.ts
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chore: import upstream snapshot with attribution
2026-07-13 13:00:43 +08:00

38 lines
1.4 KiB
TypeScript

/**
* Auto-grow a controlled textarea so it fits its content from a single
* line up to a fixed maximum, after which it scrolls. Sharing one hook
* across composers keeps their sizing behavior identical — divergent
* imperative implementations have previously caused subtle keystroke
* bugs (e.g. height not shrinking after Backspace on a Shift+Enter
* line).
*
* The reset uses ``height: auto`` (not a fixed minimum) so the browser
* recomputes ``scrollHeight`` from the actual content rather than from
* a stale clipped value — that was the source of the prior shrink bug.
*/
import { useLayoutEffect, type RefObject } from "react";
export interface AutoSizedTextareaOptions {
/** Minimum height in pixels (clamps ``scrollHeight`` from below). */
min?: number;
/** Maximum height in pixels; beyond this the textarea scrolls. */
max?: number;
}
export function useAutoSizedTextarea(
ref: RefObject<HTMLTextAreaElement | null>,
value: string,
{ min = 0, max = Number.POSITIVE_INFINITY }: AutoSizedTextareaOptions = {},
): void {
useLayoutEffect(() => {
const el = ref.current;
if (!el) return;
el.style.height = "auto";
const natural = el.scrollHeight;
const bounded = Math.min(Math.max(natural, min), max);
el.style.height = `${bounded}px`;
el.style.overflowY = natural > max ? "auto" : "hidden";
}, [ref, value, min, max]);
}