Cursor rule

1---
2alwaysApply: false
3---
4 
5## Defer Await Until Needed
6 
7Move `await` operations into the branches where they're actually used to avoid blocking code paths that don't need them.
8 
9**Incorrect (blocks both branches):**
10 
11```typescript
12async function handleRequest(userId: string, skipProcessing: boolean) {
13  const userData = await fetchUserData(userId)
14  
15  if (skipProcessing) {
16    // Returns immediately but still waited for userData
17    return { skipped: true }
18  }
19  
20  // Only this branch uses userData
21  return processUserData(userData)
22}
23```
24 
25**Correct (only blocks when needed):**
26 
27```typescript
28async function handleRequest(userId: string, skipProcessing: boolean) {
29  if (skipProcessing) {
30    // Returns immediately without waiting
31    return { skipped: true }
32  }
33  
34  // Fetch only when needed
35  const userData = await fetchUserData(userId)
36  return processUserData(userData)
37}
38```
39 
40**Another example (early return optimization):**
41 
42```typescript
43// Incorrect: always fetches permissions
44async function updateResource(resourceId: string, userId: string) {
45  const permissions = await fetchPermissions(userId)
46  const resource = await getResource(resourceId)
47  
48  if (!resource) {
49    return { error: 'Not found' }
50  }
51  
52  if (!permissions.canEdit) {
53    return { error: 'Forbidden' }
54  }
55  
56  return await updateResourceData(resource, permissions)
57}
58 
59// Correct: fetches only when needed
60async function updateResource(resourceId: string, userId: string) {
61  const resource = await getResource(resourceId)
62  
63  if (!resource) {
64    return { error: 'Not found' }
65  }
66  
67  const permissions = await fetchPermissions(userId)
68  
69  if (!permissions.canEdit) {
70    return { error: 'Forbidden' }
71  }
72  
73  return await updateResourceData(resource, permissions)
74}
75```
76 
77This optimization is especially valuable when the skipped branch is frequently taken, or when the deferred operation is expensive.
78 
79For `await getFlag()` combined with a cheap synchronous guard (`flag && someCondition`), see [Check Cheap Conditions Before Async Flags](./async-cheap-condition-before-await.md).
80