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fix: clamp markdown cursor range offsets #770

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Merged
jmusial merged 2 commits into from
Jul 29, 2026
+17 −2
Merged

fix: clamp markdown cursor range offsets #770

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8c9aeb5
fix: clamp markdown cursor range offsets
x-dev90 Jul 24, 2026
a572dff
fix: update documentation for clamping cursor range offsets
x-dev90 Jul 29, 2026
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19 changes: 17 additions & 2 deletions src/web/utils/cursorUtils.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,19 @@ import {isChildOfMultilineMarkdownElement} from './blockUtils';
import {findHTMLElementInTree, getTreeNodeByIndex} from './treeUtils';
import type {TreeNode} from './treeUtils';

function getMaxRangeOffset(node: ChildNode): number {
return node.nodeType === Node.TEXT_NODE ? (node.textContent ?? '').length : node.childNodes.length;
}

/**
* Range offsets are applied to the real DOM node, not the parsed markdown tree.
* When the tree is temporarily stale, clamp to the DOM node's bounds so cursor
* restoration lands at the nearest valid position instead of throwing.
*/
function getClampedRangeOffset(node: ChildNode, offset: number): number {

@jmusial jmusial Jul 28, 2026

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Would be good to have jsdoc here with some context.

return Math.max(0, Math.min(offset, getMaxRangeOffset(node)));
}

function setCursorPosition(target: MarkdownTextInputElement, startIndex: number, endIndex: number | null = null, shouldScrollIntoView = false) {
// We don't want to move the cursor if the target is not focused
if (!target.tree || target !== document.activeElement) {
Expand All @@ -29,14 +42,16 @@ function setCursorPosition(target: MarkdownTextInputElement, startIndex: number,
range.setStartBefore(startTreeNode.element);
} else {
const startElement = startTreeNode.element;
range.setStart((startElement.childNodes[0] || startElement) as ChildNode, start - startTreeNode.start);
const startNode = (startElement.childNodes[0] || startElement) as ChildNode;
range.setStart(startNode, getClampedRangeOffset(startNode, start - startTreeNode.start));
}

if (endTreeNode.type === 'br') {
range.setEndBefore(endTreeNode.element);
} else {
const endElement = endTreeNode.element;
range.setEnd((endElement.childNodes[0] || endElement) as ChildNode, (end || start) - endTreeNode.start);
const endNode = (endElement.childNodes[0] || endElement) as ChildNode;
range.setEnd(endNode, getClampedRangeOffset(endNode, (end || start) - endTreeNode.start));
}

if (!end) {
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