Next.js quickstart

1. Install hypertune

Once you have a Next.js application ready, install Hypertune's JavaScript SDK:

npm

npm install hypertune

yarn

yarn add hypertune

pnpm

pnpm add hypertune

2. Set environment variables

Define the following environment variables in your .env file:

NEXT_PUBLIC_HYPERTUNE_TOKEN=token
HYPERTUNE_OUTPUT_FILE_PATH=generated/hypertune.ts

Replace token with your project token which you can find in the Settings tab of your project.

3. Generate the client

Generate a type-safe client to access your flags by running:

npm

npx hypertune

yarn

yarn hypertune

pnpm

pnpm hypertune

4. Use the client

Add a new file called hypertune.ts that creates and exports a hypertune singleton:

import { initHypertune } from "./generated/hypertune";

const hypertune = initHypertune({
  token: process.env.NEXT_PUBLIC_HYPERTUNE_TOKEN!,
});

export default hypertune;

Then import and use this hypertune singleton to access your flags with end-to-end type-safety:

App Router

To access flags in React Server Components (RSC), use the hypertune singleton directly:

import ClientExample from "./ClientExample";
import hypertune from "./hypertune";

export default async function ServerExample() {
  await hypertune.initFromServerIfNeeded();

  const rootNode = hypertune.root({
    args: {
      context: {
        environment: "DEVELOPMENT",
        user: { id: "test_id", name: "Test", email: "[e-mail]" },
      },
    },
  });

  const exampleFlag = rootNode.exampleFlag({ fallback: false });

  return (
    <>
      <div>Server Component flag: {String(exampleFlag)}</div>
      <ClientExample hypertuneDehydratedState={hypertune.dehydrate()} />
    </>
  );
}

To access flags in Client Components (RCC), first define a useHypertune hook in a new file called useHypertune.ts:

import React, { useEffect, useMemo } from "react";
import hypertune from "./hypertune";

export default function useHypertune() {
  // Trigger a re-render when flags are updated
  const [, setStateHash] = React.useState<string | null>(
    hypertune.getStateHash()
  );
  useEffect(() => {
    hypertune.addUpdateListener(setStateHash);
    return () => {
      hypertune.removeUpdateListener(setStateHash);
    };
  }, []);

  // Return the Hypertune root node initialized with the current user
  return useMemo(
    () =>
      hypertune.root({ 
        args:{
          context: {
            environment: "DEVELOPMENT",
            user: { id: "test_id", name: "Test", email: "[e-mail]" },
          },
        },
      }),
    []
  );
}

Then use the hook:

"use client";

import { DehydratedState } from "../generated/hypertune";
import hypertune from "./hypertune";
import useHypertune from "./useHypertune";

export default function ClientExample({
  hypertuneDehydratedState,
}: {
  hypertuneDehydratedState?: DehydratedState | null;
}): React.ReactElement {
  if (hypertuneDehydratedState) {
    hypertune.hydrate(hypertuneDehydratedState);
  }

  const rootNode = useHypertune();

  const exampleFlag = rootNode.exampleFlag({ fallback: false });

  return <div>Client Component flag: {String(exampleFlag)}</div>;
}

Pages Router

To access flags in getServerSideProps or getStaticProps for Server-side Rendering (SSR), Static Site Generation (SSG) or Incremental Static Regeneration (ISR), use the hypertune singleton directly:

import { GetServerSideProps, InferGetServerSidePropsType } from "next";
import React from "react";
import { DehydratedState } from "../generated/hypertune";
import hypertune from "../lib/hypertune";
import ClientExample from "../lib/ClientExample";

export const getServerSideProps = (async (context) => {
  await hypertune.initIfNeeded();

  const rootNode = hypertune.root({
    args: {
      context: {
        environment: "DEVELOPMENT",
        user: { id: "test_id", name: "Test", email: "[e-mail]" },
      },
    },
  });

  const exampleFlag = rootNode.exampleFlag({ fallback: false });

  return {
    props: { exampleFlag, hypertuneDehydratedState: hypertune.dehydrate() },
  };
}) satisfies GetServerSideProps<{
  exampleFlag: boolean;
  hypertuneDehydratedState: DehydratedState | null;
}>;

export default function Page({
  exampleFlag,
  hypertuneDehydratedState,
}: InferGetServerSidePropsType<typeof getServerSideProps>): React.ReactElement {
  return (
    <>
      <div>Server Side Props flag: {String(exampleFlag)}</div>
      <ClientExample hypertuneDehydratedState={hypertuneDehydratedState} />
    </>
  );
}

To access flags on the client for Client-side Rendering (CSR), first define a useHypertune hook in a new file called useHypertune.ts:

import React, { useEffect, useMemo } from "react";
import hypertune from "./hypertune";

export default function useHypertune() {
  // Trigger a re-render when flags are updated
  const [, setStateHash] = React.useState<string | null>(
    hypertune.getStateHash(),
  );
  useEffect(() => {
    hypertune.addUpdateListener(setStateHash);
    return () => {
      hypertune.removeUpdateListener(setStateHash);
    };
  }, []);

  // Return the Hypertune root node initialized with the current user
  return useMemo(
    () =>
      hypertune.root({
        args: {
          context: {
            environment: "DEVELOPMENT",
            user: { id: "test_id", name: "Test", email: "[e-mail]" },
          },
        },
      }),
    [],
  );
}

Then use the hook in your page or component:

import { DehydratedState } from "../generated/hypertune";
import hypertune from "./hypertune";
import useHypertune from "./useHypertune";

export default function ClientExample({
  hypertuneDehydratedState,
}: {
  hypertuneDehydratedState?: DehydratedState | null;
}): React.ReactElement {
  if (hypertuneDehydratedState) {
    hypertune.hydrate(hypertuneDehydratedState);
  }

  const rootNode = useHypertune();

  const exampleFlag = rootNode.exampleFlag({ fallback: false });

  return <div>Client Component flag: {String(exampleFlag)}</div>;
}

Edge Middleware

To access flags in Edge Middleware, use the hypertune singleton directly:

import { NextFetchEvent, NextRequest } from "next/server";
import hypertune from "./lib/hypertune";

export const config = {
  matcher: "/",
};

export async function middleware(
  req: NextRequest,
  context: NextFetchEvent
): Promise<void> {
  await hypertune.initIfNeeded();

  const rootNode = hypertune.root({
    args: {
      context: {
        environment: "DEVELOPMENT",
        user: { id: "test", name: "Test", email: "[e-mail]" },
      },
    },
  });
  const exampleFlag = rootNode.exampleFlag({ fallback: false });
  console.log("Edge Middleware flag:", exampleFlag);

  context.waitUntil(hypertune.flushLogs());
}

Edge and Serverless Functions

To access flags in Edge Functions and Serverless Functions, use the hypertune singleton directly:

import { NextResponse } from "next/server";
import hypertune from "../../../lib/hypertune";

export const runtime = "edge";
export const dynamic = "force-dynamic";

export async function GET(): Promise<NextResponse> {
  await hypertune.initIfNeeded();

  const rootNode = hypertune.root({
    args: {
      context: {
        environment: "DEVELOPMENT",
        user: { id: "test", name: "Test", email: "[e-mail]" },
      },
    },
  });
  const exampleFlag = rootNode.exampleFlag({ fallback: false });
  console.log("Edge Functions flag:", exampleFlag);

  return NextResponse.json({ exampleFlag });
}

Notice how we passed the ClientExample component a prop with the result of hypertune.dehydrate() on the server. This shows how you can immediately "bootstrap" the SDK on the client with the state of the SDK from the server. This lets you use your flag in the first app render without any page load delay, UI flicker or layout shift. This is optional; if you don't bootstrap the SDK on the client in this way, it will initialize as usual in the background and the useHypertune hook will trigger a re-render when it's done.

If you're using Hypertune in the browser and have a Content Security Policy, add the following URLs to the connect-src directive: https://edge.hypertune.com https://gcp.fasthorse.workers.dev

This allows analytics to be sent back to Hypertune so you can see how often different parts of your flag logic are called, e.g. to see how many sessions fall into each targeting rule, as well as analytics for your events, A/B tests and machine learning loops.

5. (Optional) Include a build-time logic snapshot

If you don't "bootstrap" the SDK on the client with the state of the SDK from the server, as described above, and you try accessing your flag on the first app render, you'll get your hardcoded fallback value if the SDK hasn't had a chance to initialize from Hypertune Edge yet. This can result in a UI flicker or layout shift if the flag value changes when the SDK initializes. To avoid this, you can include a snapshot of your flag logic in the generated client as a build-time snapshot.

Add the following environment variable to your .env file:

HYPERTUNE_INCLUDE_INIT_DATA=true

Then regenerate the client.

The SDK will now instantly initialize from the snapshot first before fetching the latest flag logic from Hypertune Edge. And it will always successfully initialize, even if Hypertune Edge is unreachable. You can keep the snapshot fresh by setting up a webhook to regenerate the client on every Hypertune commit.

If you don't want to include the snapshot but still want to avoid UI flickers and layout shift, you can explicitly wait for initialization from Hypertune Edge with await hypertune.initIfNeeded() or check for initialization from Hypertune Edge with !!hypertune.getLastDataProviderInitTime().

6. (Optional) Use Vercel Edge Config

If your Next.js app is deployed on Vercel, you can use Edge Config to initialize the Hypertune SDK on the server with near-zero latency.

1. Install the integration

1. Go to the Hypertune page in the Vercel Integrations marketplace and click "Add Integration".

2. Select your Vercel team and project.

3. Continue and log into Hypertune.

4. Connect your Hypertune project to a new or existing Edge Config store. Copy the displayed environment variables for later. They contain your Hypertune Token, Edge Config Connection String and Edge Config Item Key.

5. Go to your Vercel dashboard and select the project you want to use the Hypertune integration with. Go to Settings > Environment Variables and add the following:

   1. NEXT_PUBLIC_HYPERTUNE_TOKEN, set to your Hypertune Token

   2. EDGE_CONFIG, set to your Edge Config Connection String

   3. EDGE_CONFIG_HYPERTUNE_ITEM_KEY, set to your Edge Config Item Key

2. Use the integration

Add the environment variables to your .env.development.local file by running:

vercel env pull .env.development.local

Install the Vercel Edge Config package:

npm

npm install @vercel/edge-config

yarn

yarn add @vercel/edge-config

pnpm

pnpm add @vercel/edge-config

Update your hypertune.ts to create an Edge Config client and pass it along with your Edge Config Item Key when initializing the Hypertune SDK:

import { createClient } from "@vercel/edge-config";
import { VercelEdgeConfigInitDataProvider } from "hypertune";
import { initHypertune } from "./generated/hypertune";

const hypertune = initHypertune({
  token: process.env.NEXT_PUBLIC_HYPERTUNE_TOKEN!,
  initDataProvider: 
    process.env.EDGE_CONFIG && process.env.EDGE_CONFIG_HYPERTUNE_ITEM_KEY
      ? new VercelEdgeConfigInitDataProvider({
          edgeConfigClient: createClient(process.env.EDGE_CONFIG),
          itemKey: process.env.EDGE_CONFIG_HYPERTUNE_ITEM_KEY,
        }),
      : undefined
});

export default hypertune;

That's it

Now you can update the logic for exampleFlag from the Hypertune UI without updating your code or waiting for a new build, deployment or app release.

To add a new flag, create it in the Hypertune UI then regenerate the client.