Simple Boolean Feature Flag Toggle
Create a basic boolean feature flag that turns a feature on or off for all users. The simplest and most common feature flag pattern used in production.
Detailed Explanation
Boolean Feature Flag Toggle
The boolean toggle is the most fundamental feature flag pattern. A flag is either true (feature enabled) or false (feature disabled) for all users who evaluate it.
Configuration Example
{
"dark-mode": {
"name": "Dark Mode",
"description": "Enable dark mode theme for all users",
"type": "boolean",
"enabled": true,
"defaultValue": false,
"targeting": []
}
}
How It Works
When the flag is enabled with a defaultValue of false, the feature is technically active but defaults to off. This might seem counterintuitive, but it allows you to add targeting rules later without changing the flag state. When you set defaultValue to true, all users see the feature.
Key Considerations
| Aspect | Detail |
|---|---|
| Simplicity | No targeting rules needed for global on/off |
| Performance | Fastest evaluation since no rules are checked |
| Fallback | Always has a clear fallback value |
| Use cases | Maintenance mode, feature launches, quick rollbacks |
LaunchDarkly Equivalent
In LaunchDarkly, this maps to a flag with kind: "boolean" and two variations: [true, false]. The offVariation points to the false variation.
Best Practices
- Always set a meaningful default value that represents the "safe" state
- Use descriptive flag keys like
enable-dark-moderather thanflag-123 - Include a description that explains what the flag controls and why it exists
- Consider adding a cleanup date or ticket reference in the description
Use Case
Launching a new dark mode feature where you want a simple on/off switch. During development, the flag stays off. On launch day, flip the flag to true. If issues arise, immediately flip back to false without deploying code.