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38 lines
1.2 KiB
Markdown
38 lines
1.2 KiB
Markdown
---
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title: Check Cheap Conditions Before Async Flags
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impact: HIGH
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impactDescription: avoids unnecessary async work when a synchronous guard already fails
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tags: async, await, feature-flags, short-circuit, conditional
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---
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## Check Cheap Conditions Before Async Flags
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When a branch uses `await` for a flag or remote value and also requires a **cheap synchronous** condition (local props, request metadata, already-loaded state), evaluate the cheap condition **first**. Otherwise you pay for the async call even when the compound condition can never be true.
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This is a specialization of [Defer Await Until Needed](./async-defer-await.md) for `flag && cheapCondition` style checks.
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**Incorrect:**
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```typescript
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const someFlag = await getFlag()
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if (someFlag && someCondition) {
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// ...
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}
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```
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**Correct:**
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```typescript
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if (someCondition) {
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const someFlag = await getFlag()
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if (someFlag) {
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// ...
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}
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}
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```
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This matters when `getFlag` hits the network, a feature-flag service, or `React.cache` / DB work: skipping it when `someCondition` is false removes that cost on the cold path.
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Keep the original order if `someCondition` is expensive, depends on the flag, or you must run side effects in a fixed order.
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