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fix: don't restore a stale caret position onto content it wasn't computed against #37

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Merged
ryan-roemer merged 2 commits into from
Oct 16, 2026
Merged

fix: don't restore a stale caret position onto content it wasn't computed against #37

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2c81951
fix: resolve typing bug
jimthedev Sep 5, 2026
5fd1324
fix: don't restore a stale caret position onto content it wasn't comp…
jimthedev Oct 16, 2026
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54 changes: 42 additions & 12 deletions src/useEditable.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -27,6 +27,11 @@ const setCurrentRange = (range: Range) => {
const isUndoRedoKey = (event: KeyboardEvent): boolean =>
(event.metaKey || event.ctrlKey) && !event.altKey && event.code === 'KeyZ';

// contenteditable Quirk: Without plaintext-only a pre/pre-wrap element must always
// end with at least one newline character
const normalize = (content: string): string =>
content[content.length - 1] !== '\n' ? content + '\n' : content;

const toString = (element: HTMLElement): string => {
const queue: Node[] = [element.firstChild!];

Expand All @@ -43,11 +48,7 @@ const toString = (element: HTMLElement): string => {
if (node.firstChild) queue.push(node.firstChild);
}

// contenteditable Quirk: Without plaintext-only a pre/pre-wrap element must always
// end with at least one newline character
if (content[content.length - 1] !== '\n') content += '\n';

return content;
return normalize(content);
};

const setStart = (range: Range, node: Node, offset: number) => {
Expand Down Expand Up @@ -144,6 +145,20 @@ const makeRange = (
return range;
};

// Whether the DOM currently shows the content that `state.position` was computed

@ilteoood ilteoood Oct 2, 2026

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Docstring overstates the trigger. This says the bad render "can commit in between a keystroke's keydown and keyup." The guard actually runs on every render, and update, flushChanges, undo/redo, and onSelect all benefit from it. Reword to match the title: e.g. "Any render that isn't the direct result of this hook's own onChange call — e.g. one triggered by an unrelated state update elsewhere in the tree — can commit while the DOM already reflects content this hook hasn't observed yet. In the keystroke case this lands between keydown and keyup…"

// against. This runs on every render. Any render that isn't the direct result of this
// hook's own onChange call (e.g. one triggered by an unrelated state update elsewhere
// in the tree) can commit while the DOM already reflects content this hook hasn't
// observed yet. In the keystroke case that's a native edit landing between keydown and
// keyup; restoring `state.position` onto it would yank the browser's own (correct)
// cursor to the wrong place -- corrupting every keystroke that follows. Every site that
// sets `state.expectedContent` must store it in `toString`'s normalized form (see
// `normalize`) so this comparison is exact. It's left `undefined` when there's nothing
// to check against (e.g. before the first change).
const matchesExpectedContent = (element: HTMLElement, state: State): boolean =>
state.expectedContent === undefined ||
toString(element) === state.expectedContent;

interface State {
observer: MutationObserver;
disconnected: boolean;
Expand All @@ -152,6 +167,9 @@ interface State {
history: History[];
historyAt: number;
position: Position | null;
/** The content the DOM is expected to show once `position` is applied to it.

@ilteoood ilteoood Oct 2, 2026

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Style nit: JSDoc vs // drift. This uses /** … */ while matchesExpectedContent (lines 147-156) and the rest of the file use //. Stick with // to match the file's convention.

* Used to detect a render that doesn't correspond to `position`, see below. */
expectedContent: string | undefined;
}

export interface Options {
Expand Down Expand Up @@ -187,6 +205,7 @@ export const useEditable = (
history: [],
historyAt: -1,
position: null,
expectedContent: undefined,
};

if (typeof MutationObserver !== 'undefined') {
Expand All @@ -205,11 +224,20 @@ export const useEditable = (
if (element) {
const position = getPosition(element);
const prevContent = toString(element);
position.position += content.length - prevContent.length;
// Compare like with like: the DOM will read back with a trailing newline
// (see toString), so a caller passing content without one would otherwise
// get a caret delta that's off by one and an expectedContent that never matches
const nextContent = normalize(content);
position.position += nextContent.length - prevContent.length;
state.position = position;
state.expectedContent = nextContent;
state.onChange(content, position);
}
},
// Mutates the DOM directly and places the caret itself, so it deliberately doesn't
// touch state.position / state.expectedContent. If a render lands before the next
// flushChanges(), matchesExpectedContent() sees the DOM has moved on and leaves the
// caret where insert() put it, which is what we want.
insert(append: string, deleteOffset?: number) {
const { current: element } = elementRef;
if (element) {
Expand Down Expand Up @@ -262,7 +290,7 @@ export const useEditable = (

state.disconnected = false;
state.observer.observe(elementRef.current, observerSettings);
if (state.position) {
if (state.position && matchesExpectedContent(elementRef.current, state)) {

@ilteoood ilteoood Oct 2, 2026

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Per-render toString cost. This check (and the identical one at line 301) calls toString(element) on every render. toString walks the full DOM (lines 24-49). For long editors this doubles per-render stringification work on top of the walks already done elsewhere. Optional optimization: short-circuit by comparing element.textContent first and only walk when that suggests divergence.

const { position, extent } = state.position;
setCurrentRange(
makeRange(elementRef.current, position, position + extent)
Expand All @@ -282,7 +310,7 @@ export const useEditable = (
}

const element = elementRef.current!;
if (state.position) {
if (state.position && matchesExpectedContent(element, state)) {
element.focus();
const { position, extent } = state.position;
setCurrentRange(makeRange(element, position, position + extent));
Expand Down Expand Up @@ -349,6 +377,7 @@ export const useEditable = (
disconnect();
const content = toString(element);
state.position = position;
state.expectedContent = content;

@ilteoood ilteoood Oct 2, 2026

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flushChanges only updates state.position/state.expectedContent when state.queue.length > 0. Combined with the expectedContent === undefined short-circuit at line 156, a no-op flushChanges (after the first one has fired) leaves expectedContent === undefined, so the next render's guard returns true unconditionally.

Intentional per the matchesExpectedContent docstring ("before the first change"), but worth flagging: if you ever want defense-in-depth on browser-emitted native edits that produce empty mutation batches (rare, browser-dependent), you'd need this branch to set state.expectedContent unconditionally too.

let mutation: MutationRecord | void;
let i = 0;
while ((mutation = state.queue.pop())) {
Expand Down Expand Up @@ -397,6 +426,7 @@ export const useEditable = (
if (history) {
disconnect();
state.position = history[0];
state.expectedContent = history[1];
state.onChange(history[1], history[0]);
}
return;
Expand Down Expand Up @@ -459,10 +489,10 @@ export const useEditable = (

const onSelect = (event: Event) => {
// Chrome Quirk: The contenteditable may lose its selection immediately on first focus
state.position =
window.getSelection()!.rangeCount && event.target === element
? getPosition(element)
: null;
const hasSelection =
window.getSelection()!.rangeCount && event.target === element;
state.position = hasSelection ? getPosition(element) : null;
state.expectedContent = hasSelection ? toString(element) : undefined;
};

const onPaste = (event: HTMLElementEventMap['paste']) => {
Expand Down
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