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feat: empty equal cell style refactor #18
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Summary of Changes
Hello @utkuakyuz, I'm Gemini Code Assist1 ! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!
This pull request significantly improves the user experience of the diff viewer by providing a clear visual indication for empty but equal cells. By dynamically applying a new grid-based style, it ensures consistent and accurate representation of diff content, particularly within virtualized environments, directly resolving a reported UI issue.
Highlights
- Enhanced Empty Cell Visualization: Introduces a distinct visual style for empty equal cells within the diff viewer, utilizing a CSS grid pattern to clearly represent their presence, addressing the requirement from issue #17.
- Dynamic Styling for Virtualized Diffs: Implements a MutationObserver to dynamically apply the new empty cell styling. This ensures that the visual enhancements are correctly rendered and maintained even as new rows are loaded or re-rendered in the virtualized diff viewer.
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Code Review
This pull request introduces a new visual style for empty cells in the diff viewer, which is a great enhancement for usability. The implementation uses a MutationObserver to apply styles dynamically. However, the current approach has some performance and robustness issues. My review provides a detailed suggestion to refactor the MutationObserver for better performance and more reliable element selection. Additionally, I've included a comment on a CSS property that might produce an unintended visual effect.
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The current MutationObserver implementation can cause performance issues on large diffs and relies on fragile selectors.
- Performance: On every DOM change (e.g., scrolling in the virtualized list), the observer callback re-queries the entire component for
td.line-equalelements and iterates over all of them. This is inefficient and can lead to UI lag. A better approach is to process only the newly added nodes provided by theMutationObserver. - Fragile Selector: The logic to identify the right-side cell using
index % 2 === 1is implicit. It assumes a flat list of<td>elements in a specific order, which can easily break. It's more robust to use a specific CSS selector like:nth-child(4)to target the right-side content cell within its row. - Type Safety: Casting
outerRef.currentwithas HTMLElementis less safe than using aninstanceoftype guard.
I suggest refactoring this useEffect to be more performant and robust by processing only added nodes and using more specific selectors.
useEffect(() => {
const container = outerRef.current;
if (!(container instanceof HTMLElement)) {
return;
}
const observer = new MutationObserver((mutations) => {
for (const mutation of mutations) {
if (mutation.type !== "childList") {
continue;
}
for (const node of mutation.addedNodes) {
if (!(node instanceof HTMLElement)) {
continue;
}
const rightCell = node.querySelector<HTMLTableCellElement>(
".json-diff-viewer td.line-equal:nth-child(4)",
);
if (rightCell) {
const spans = rightCell.querySelectorAll("pre > span");
if (spans.length === 1 && spans[0].textContent?.trim() === "") {
rightCell.classList.add("empty-equal-cell");
}
}
}
}
});
observer.observe(container, { childList: true, subtree: true });
return () => observer.disconnect();
}, []);
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I cannot apply this because this creates a new display bug when expanding hidden lines. When user clicks on expand button, new displayed rows shown with background pattern. This is not wanted. Optimization may be considered in the future if any idea comes up.
Empty cells shown with a CSS grid same as in the example of issue #17
imageResolves #17