A lightweight Express.js middleware to help you implement feature flags. Easily manage and restrict access to routes based on static or dynamic flags, supporting both synchronous and asynchronous evaluation.
- Simple API for defining feature flags
- Support for static and async flag evaluation
- Restrict access to routes based on flags
- Environment variable integration
- TypeScript support out of the box
npm install trunkerimport express from "express";
import { createTrunker } from "trunker";
const app = express();
const trunker = createTrunker({
flags: {
betaFeature: { active: true },
legacyMode: { active: false },
},
});
app.use(trunker.middleware());
// this route is accessible because betaFeature is active
app.get("/beta", trunker.restrict("betaFeature"), (req, res) => {
res.send("Beta feature is enabled!");
});
// this route is not accessible because legacyMode is not active
app.get("/legacy", trunker.restrict("legacyMode"), (req, res) => {
res.send("Legacy mode is enabled!");
});
app.listen(3000);You can restrict access to routes using the restrict middleware:
app.get(
"/admin",
trunker.restrict("betaFeature"),
(req, res) => {
res.send("Admin route with beta feature enabled");
}
);You can also restrict by multiple flags:
app.get(
"/multi",
trunker.restrict(["betaFeature", "legacyMode"]),
(req, res) => {
res.send("Route with multiple flags");
}
);import { fromEnv, createTrunker } from "trunker";
const trunker = createTrunker(fromEnv(process.env));Environment variables should be prefixed with TRUNKER_, e.g.:
TRUNKER_BETA=true
TRUNKER_LEGACY=false
flags: {
premiumUser: {
active: async (req) => {
// Custom logic, e.g., check user subscription
return await checkUserSubscription(req.user);
},
},
}import { isFlagActive } from "trunker";
app.get("/some-route", async (req, res) => {
if (await isFlagActive(req, "betaFeature")) {
res.send("Feature enabled");
} else {
res.status(403).send("Not available");
}
});You can customize the error response format:
const trunker = createTrunker({
flags: { ... },
error: {
format: "json", // required. `json` or `plain`
key: "message", // optional
statusCode: 403, // optional
template: "You can't access this route: {{flag}} is disabled" // optional
},
});Creates the middleware. Pass an object with a flags property. Returns an object with middleware() and restrict() methods.
Generates flag configuration from environment variables.
Checks if a flag is active for the current request.
Express middleware to attach flags to req.trunker.
Express middleware to restrict access based on one or more flags.
The middleware adds a trunker property to the Express Request type. You may need to import the type definitions for full type safety.
import { type Flags } from "trunker";
declare module "express-serve-static-core" {
interface Request {
trunker: Flags;
}
}MIT