mirror of
https://github.com/kjanat/livedash-node.git
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Kaj Kowalski
cd05fc8648
- Fix syntax errors in skills markdown files (.github/skills, .opencode/skills) - Change typescript to tsx for code blocks with JSX - Replace ellipsis (...) in array examples with valid syntax - Separate CSS from TypeScript into distinct code blocks - Convert JavaScript object examples to valid JSON in docs - Fix enum definitions with proper comma separation
58 lines
1.6 KiB
Markdown
58 lines
1.6 KiB
Markdown
---
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title: Batch DOM CSS Changes
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impact: MEDIUM
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impactDescription: reduces reflows/repaints
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tags: javascript, dom, css, performance, reflow
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---
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## Batch DOM CSS Changes
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Avoid interleaving style writes with layout reads. When you read a layout property (like `offsetWidth`, `getBoundingClientRect()`, or `getComputedStyle()`) between style changes, the browser is forced to trigger a synchronous reflow.
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**Incorrect (interleaved reads and writes force reflows):**
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```typescript
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function updateElementStyles(element: HTMLElement) {
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element.style.width = "100px";
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const width = element.offsetWidth; // Forces reflow
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element.style.height = "200px";
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const height = element.offsetHeight; // Forces another reflow
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}
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```
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**Correct (batch writes, then read once):**
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```typescript
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function updateElementStyles(element: HTMLElement) {
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// Batch all writes together
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element.style.width = "100px";
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element.style.height = "200px";
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element.style.backgroundColor = "blue";
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element.style.border = "1px solid black";
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// Read after all writes are done (single reflow)
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const { width, height } = element.getBoundingClientRect();
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}
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```
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**Better: use CSS classes**
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```css
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.highlighted-box {
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width: 100px;
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height: 200px;
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background-color: blue;
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border: 1px solid black;
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}
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```
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```typescript
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function updateElementStyles(element: HTMLElement) {
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element.classList.add("highlighted-box");
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const { width, height } = element.getBoundingClientRect();
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}
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```
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Prefer CSS classes over inline styles when possible. CSS files are cached by the browser, and classes provide better separation of concerns and are easier to maintain.
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