Managing feature flags in Express.js applications can be challenging. To simplify this process, I developed Trunker, a lightweight middleware that enables dynamic route control based on feature flags.

What is Trunker?

Trunker is a middleware for Express.js that allows you to define feature flags (either static or asynchronous) to control access to specific routes. This approach is particularly useful for implementing Trunk-Based Development, where features can be toggled without deploying new code.

Installation

Install Trunker via npm:

yarn add trunker

Usage

To use Trunker, import it into your Express.js application and define your feature flags:

import express from "express";
import { createTrunker } from "trunker";
import { getUser } from "./utils";

const app = express();
const trunker = createTrunker({
  flags: {
    betaFeature1: true,
    betaFeature2: async (req) => {
      const user = await getUser(req.body.userId);
      return user.isBetaTester
    },
  },
});

app.use(trunker.middleware());

// It can be accessed
app.get("/beta-feature1", trunker.restrict("betaFeature1"), (req, res) => {
  res.send("Hello, world! From /beta-feature1.");
});

// It cant be accessed
app.get("/beta-feature2", trunker.restrict("betaFeature2"), (req, res) => {
  res.send("Hello, world! From /beta-feature2.");
});

app.listen(3000, () => console.log("Listening on port 3000"));

In this example:

• betaFeature1 is a static flag set to true.
• betaFeature2 is an asynchronous flag that determines access based on user data.

The feature flag can be static or asynchronous. If the flag is static, it will be evaluated immediately and if it's asynchronous, it will be evaluated when the request is made. The method trunker.restrict accepts either a string or an array of strings.

You can also manually check if a feature flag is active:

import { isFlagActive } from "trunker";

app.get("/beta-feature", async (req, res) => {
  const isBetaFeatureActive = await isFlagActive(req, "betaFeature");
  if (isBetaFeatureActive) {
    res.send("Hello, world! From /beta-feature.");
  } else {
    res.status(403).send("Forbidden");
  }
});

Learn More

For detailed documentation and source code, visit the Trunker GitHub repository.Feel free to contribute, report issues, or suggest enhancements!

Por hoje é só.