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83 lines
2.2 KiB
Markdown
83 lines
2.2 KiB
Markdown
---
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title: Defer Await Until Needed
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impact: HIGH
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impactDescription: avoids blocking unused code paths
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tags: async, await, conditional, optimization
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---
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## Defer Await Until Needed
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Move `await` operations into the branches where they're actually used to avoid blocking code paths that don't need them.
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**Incorrect (blocks both branches):**
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```typescript
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async function handleRequest(userId: string, skipProcessing: boolean) {
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const userData = await fetchUserData(userId)
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if (skipProcessing) {
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// Returns immediately but still waited for userData
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return { skipped: true }
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}
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// Only this branch uses userData
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return processUserData(userData)
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}
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```
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**Correct (only blocks when needed):**
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```typescript
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async function handleRequest(userId: string, skipProcessing: boolean) {
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if (skipProcessing) {
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// Returns immediately without waiting
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return { skipped: true }
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}
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// Fetch only when needed
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const userData = await fetchUserData(userId)
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return processUserData(userData)
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}
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```
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**Another example (early return optimization):**
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```typescript
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// Incorrect: always fetches permissions
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async function updateResource(resourceId: string, userId: string) {
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const permissions = await fetchPermissions(userId)
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const resource = await getResource(resourceId)
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if (!resource) {
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return { error: 'Not found' }
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}
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if (!permissions.canEdit) {
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return { error: 'Forbidden' }
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}
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return await updateResourceData(resource, permissions)
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}
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// Correct: fetches only when needed
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async function updateResource(resourceId: string, userId: string) {
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const resource = await getResource(resourceId)
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if (!resource) {
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return { error: 'Not found' }
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}
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const permissions = await fetchPermissions(userId)
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if (!permissions.canEdit) {
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return { error: 'Forbidden' }
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}
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return await updateResourceData(resource, permissions)
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}
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```
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This optimization is especially valuable when the skipped branch is frequently taken, or when the deferred operation is expensive.
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For `await getFlag()` combined with a cheap synchronous guard (`flag && someCondition`), see [Check Cheap Conditions Before Async Flags](./async-cheap-condition-before-await.md).
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