feature-flags

Original：🇺🇸 English

Translated

Use when feature flag tests fail, flags need updating, understanding @gate pragmas, debugging channel-specific test failures, or adding new flags to React.

2installs

Sourcefacebook/react

Added on2026-02-04

NPX Install

npx skill4agent add facebook/react feature-flags

SKILL.md Content

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React Feature Flags

Flag Files

File	Purpose
`packages/shared/ReactFeatureFlags.js`	Default flags (canary), `__EXPERIMENTAL__` overrides
`packages/shared/forks/ReactFeatureFlags.www.js`	www channel, `__VARIANT__` overrides
`packages/shared/forks/ReactFeatureFlags.native-fb.js`	React Native, `__VARIANT__` overrides
`packages/shared/forks/ReactFeatureFlags.test-renderer.js`	Test renderer

Gating Tests

@gate

pragma (test-level)

Use when the feature is completely unavailable without the flag:

javascript

// @gate enableViewTransition
it('supports view transitions', () => {
  // This test only runs when enableViewTransition is true
  // and is SKIPPED (not failed) when false
});

gate()

inline (assertion-level)

Use when the feature exists but behavior differs based on flag:

javascript

it('renders component', async () => {
  await act(() => root.render(<App />));

  if (gate(flags => flags.enableNewBehavior)) {
    expect(container.textContent).toBe('new output');
  } else {
    expect(container.textContent).toBe('legacy output');
  }
});

Adding a New Flag

Add to
```
ReactFeatureFlags.js
```
with default value
Add to each fork file (
```
*.www.js
```
,
```
*.native-fb.js
```
, etc.)
If it should vary in www/RN, set to
```
__VARIANT__
```
in the fork file
Gate tests with
```
@gate flagName
```
or inline
```
gate()
```

Checking Flag States

Use

/flags

to view states across channels. See the

flags

skill for full command options.

__VARIANT__

Flags (GKs)

Flags set to

__VARIANT__

simulate gatekeepers - tested twice (true and false):

bash

/test www <pattern>              # __VARIANT__ = true
/test www variant false <pattern> # __VARIANT__ = false

Debugging Channel-Specific Failures

Run
```
/flags --diff <channel1> <channel2>
```
to compare values
Check
```
@gate
```
conditions - test may be gated to specific channels
Run
```
/test <channel> <pattern>
```
to isolate the failure
Verify flag exists in all fork files if newly added

Common Mistakes

Forgetting both variants - Always test
```
www
```
AND
```
www variant false
```
for
```
__VARIANT__
```
flags
Using @gate for behavior differences - Use inline
```
gate()
```
if both paths should run
Missing fork files - New flags must be added to ALL fork files, not just the main one
Wrong gate syntax - It's
```
gate(flags => flags.name)
```
, not
```
gate('name')
```