struxadotcloud/struxa

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initial commitd4cb9e15 months ago37 lines · 1.2 KB

1	---
2	title: Check Cheap Conditions Before Async Flags
3	impact: HIGH
4	impactDescription: avoids unnecessary async work when a synchronous guard already fails
5	tags: async, await, feature-flags, short-circuit, conditional
6	---
7
8	## Check Cheap Conditions Before Async Flags
9
10	When a branch uses `await` for a flag or remote value and also requires a **cheap synchronous
11
12	This is a specialization of [Defer Await Until Needed](./async-defer-await.md
13
14	Incorrect:
15
16	```typescript
17	const someFlag = await
18
19	if (someFlag && someCondition
20	// ...
21	}
22	```
23
24	Correct:
25
26	```typescript
27	if (someCondition) {
28	const someFlag =
29	if (someFlag) {
30	// ...
31	}
32	}
33	```
34
35	This matters when `getFlag` hits the network, a feature-flag service, or `React.cache` / DB work: skipping it when
36
37	Keep the original order if `someCondition` is expensive, depends on the flag, or you must run side effects in a fixed order.

**

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.

)

for

`

flag && cheapCondition

`

style checks.

getFlag

()

;

)

{

await

getFlag

()

;

`

someCondition

`

is false removes that cost on the cold path.