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
43 lines
1.0 KiB
Markdown
43 lines
1.0 KiB
Markdown
---
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title: Hoist RegExp Creation
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impact: LOW-MEDIUM
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impactDescription: avoids recreation
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tags: javascript, regexp, optimization, memoization
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---
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## Hoist RegExp Creation
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Don't create RegExp inside render. Hoist to module scope or memoize with `useMemo()`.
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**Incorrect (new RegExp every render):**
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```tsx
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function Highlighter({ text, query }: Props) {
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const regex = new RegExp(`(${query})`, "gi");
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const parts = text.split(regex);
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return <>{parts.map((part, i) => part)}</>;
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}
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```
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**Correct (memoize or hoist):**
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```tsx
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const EMAIL_REGEX = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
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function Highlighter({ text, query }: Props) {
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const regex = useMemo(() => new RegExp(`(${escapeRegex(query)})`, "gi"), [query]);
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const parts = text.split(regex);
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return <>{parts.map((part, i) => part)}</>;
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}
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```
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**Warning (global regex has mutable state):**
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Global regex (`/g`) has mutable `lastIndex` state:
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```typescript
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const regex = /foo/g;
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regex.test("foo"); // true, lastIndex = 3
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regex.test("foo"); // false, lastIndex = 0
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```
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