JavaScript quickstart

1. Install hypertune

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

npm install hypertune

2. Set environment variables

Define the following environment variables in your .env file:


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:

npx 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.HYPERTUNE_TOKEN!,

export default hypertune;

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

import express from "express";
import hypertune from "./hypertune";

async function main() {
  await hypertune.initIfNeeded();

  const rootNode = hypertune.root({
    args: {
      context: {
        environment: "DEVELOPMENT",
        user: { id: "test_id", name: "Test", email: "" },

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

If you're using Hypertune in the browser and have a Content Security Policy, add the following URLs to the connect-src directive:

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 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:


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().

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, app release or service restart.

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

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