05_openfeature_with_targeting.js

import express from "express";
import cowsay from "cowsay";
import { OpenFeature, InMemoryProvider } from "@openfeature/server-sdk";

const app = express();
const routes = express.Router();
app.use((_, res, next) => {
  res.setHeader("content-type", "text/plain");
  next();
}, routes);

const featureFlags = OpenFeature.getClient();

const FLAG_CONFIGURATION = {
  'with-cows': {
    variants: {
      on: true,
      off: false
    },
    disabled: false,
    defaultVariant: "off",
    contextEvaluator: (context) => {
      if (context.cow === "Bessie") {
        return "on";
      }
      return "off";
    },
  }
};

const featureFlagProvider = new InMemoryProvider(FLAG_CONFIGURATION);

OpenFeature.setProvider(featureFlagProvider);

routes.get("/", async (req, res) => {
  const context = {
    cow: req.get("x-cow")
  };
  const withCows = await featureFlags.getBooleanValue("with-cows", false, context);
  if (withCows) {
    res.send(cowsay.say({ text: "Hello, world!" }));
  } else {
    res.send("Hello, world!");
  }
});

app.listen(3333, () => {
  console.log("Server running at http://localhost:3333");
});