Hoist RegExp Creation
Don't create RegExp inside render. Hoist to module scope or memoize with useMemo().
Incorrect (new RegExp every render):
function Highlighter({ text, query }: Props) {
const regex = new RegExp(`(${query})`, 'gi')
const parts = text.split(regex)
return <>{parts.map((part, i) => ...)}</>
}
Correct (memoize or hoist):
const EMAIL_REGEX = /^[^\s@]+@[^\s@]+\.[^\s@]+$/
function Highlighter({ text, query }: Props) {
const regex = useMemo(
() => new RegExp((${escapeRegex(query)}), 'gi'),
[query]
)
const parts = text.split(regex)
return <>{parts.map((part, i) => ...)}</>
}
**Warning (global regex has mutable state):**
Global regex (`/g`) has mutable `lastIndex` state:
```typescript
const regex = /foo/g
regex.test('foo') // true, lastIndex = 3
regex.test('foo') // false, lastIndex = 0