mirror of
https://github.com/vercel/flags.git
synced 2026-09-19 03:49:23 +08:00
Dominik Ferber
84 lines
2.5 KiB
Markdown
84 lines
2.5 KiB
Markdown
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# Flags SDK
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The feature flags toolkit for Next.js and SvelteKit.
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From the creators of Next.js, the Flags SDK is a free open-source library that gives you the tools you need to use feature flags in Next.js and SvelteKit applications.
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- Works with any flag provider, custom setups or no flag provider at all
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- Compatible with App Router, Pages Router, and Routing Middleware
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- Built for feature flags and experimentation
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See [flags-sdk.dev](https://flags-sdk.dev/) for full docs and examples.
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> Upgrading from version 3? See the [Upgrade to v4](https://github.com/vercel/flags/blob/main/packages/flags/guides/upgrade-to-v4.md) guide.
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## Installation
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Install the package using your package manager:
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```sh
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npm install flags
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```
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## Setup
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Create an environment variable called `FLAGS_SECRET`.
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The `FLAGS_SECRET` value must have a specific length (32 random bytes encoded in base64) to work as an encryption key. Create one using node:
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```sh
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node -e "console.log(crypto.randomBytes(32).toString('base64url'))"
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```
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Use a separate `FLAGS_SECRET` value for each environment (Development, Preview, Production), and mark the Preview and Production values as Sensitive. Run the generator once per environment to produce distinct values, then store each on Vercel:
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```sh
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vercel env add FLAGS_SECRET production --sensitive --value <production-secret>
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vercel env add FLAGS_SECRET preview --sensitive --value <preview-secret>
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vercel env add FLAGS_SECRET development --value <development-secret>
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```
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This secret is required to use the SDK. It is used to read overrides and to encrypt flag values in case they are sent to the client and should stay secret.
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## Usage
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Create a file called flags.ts in your project and declare your first feature flag there:
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```ts
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// app/flags.tsx
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import { flag } from "flags/next";
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export const exampleFlag = flag<boolean>({
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key: "example-flag",
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decide() {
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return true;
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},
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});
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```
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Call your feature flag in a React Server Component:
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```tsx
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// app/page.tsx
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import { exampleFlag } from "./flags";
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export default async function Page() {
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const example = await exampleFlag();
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return <div>{example ? "Flag is on" : "Flag is off"}</div>;
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}
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```
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Feature Flags can also be called in Routing Middleware and API Routes.
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## Adapters
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The Flags SDK has adapters for popular feature flag providers including LaunchDarkly, Optimizely, and Statsig.
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## Documentation
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There is a lot more to the Flags SDK than shown in the example above.
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See the full documentation and examples on [flags-sdk.dev](https://flags-sdk.dev/).
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