## <a id="update-tag"></a>22. updateTag() - Read-Your-Own-Writes
### Test Pattern: Immediate Cache Invalidation
**Test Source**: `test/e2e/app-dir/use-cache/app/(partially-static)/cache-tag/buttons.tsx` + test assertions
```typescript
"use server"
import { updateTag, revalidateTag } from "next/cache"
export async function revalidateA() {
revalidateTag("a")
}
export async function revalidateB() {
revalidateTag("b")
}
export async function revalidateC() {
revalidateTag("c")
}
// Page uses getCachedWithTag({ tag: 'a' }) and ({ tag: 'b' })
// Both also use cacheTag(tag, 'c')
// TEST BEHAVIOR (lines 223-315):
// Initial: valueA = 0.123, valueB = 0.456
//
// Call revalidateA():
// - valueA changes to 0.789
// - valueB stays 0.456
//
// Call revalidateC():
// - valueA changes (has tag 'c')
// - valueB changes (has tag 'c')
//
// This proves: Tags work as expected for granular invalidation
```
---
## <a id="revalidate-tag"></a>23. revalidateTag(tag, profile) - New Signature
### Test Pattern: Profile Parameter
**Test Source**: Documentation and recent commits show new signature
```typescript
'use server'
import { revalidateTag } from 'next/cache'
// ✅ NEW RECOMMENDED PATTERN:
export async function updateProductList() {
await db.products.update(...)
revalidateTag('products', 'max') // Stale-while-revalidate
}
// ❌ DEPRECATED (but still works):
export async function oldPattern() {
revalidateTag('products') // No profile = legacy behavior
}
// Test from use-cache.test.ts (lines 223-314):
// - Revalidate specific tags
// - Cache updates happen async
// - Stale content served while revalidating (with 'max' profile)
```
---
## <a id="refresh-api"></a>24. refresh() - Client Router Cache
### Test Pattern: In-Place Page Update
**Test Source**: `test/e2e/app-dir/use-cache/app/(partially-static)/form/page.tsx`
```typescript
import { updateTag, cacheTag } from 'next/cache'
async function refresh() {
'use server'
updateTag('home')
}
export default async function Page() {
'use cache'
cacheTag('home')
return (
<form action={refresh}>
<button id="refresh">Refresh</button>
<p id="t">{new Date().toISOString()}</p>
</form>
)
}
// ACTUAL TEST BEHAVIOR:
// 1. Initial load: timestamp = "2024-01-01T12:00:00.000Z"
// 2. Click refresh button:
// - updateTag('home') called (invalidates cache)
// - Page re-renders with new timestamp
// 3. New timestamp displayed (cache was invalidated)
//
// NOTE: This uses updateTag(), not revalidateTag()
// refresh() here is the server action name, not the next/cache function
```
---
