Gatsby quickstart

1. Install hypertune

Once you have a Gatsby 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.development and .env.production files:

.env.production

GATSBY_HYPERTUNE_TOKEN=token
HYPERTUNE_FRAMEWORK=gatsby
HYPERTUNE_OUTPUT_DIRECTORY_PATH=src/generated

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

3. Update gatsby-config.ts

Update your gatsby-config.ts to load the environment variables with dotenv:

gatsby-config.ts

import type { GatsbyConfig } from 'gatsby'

// Load environment variables
require('dotenv').config({
  path: `.env.${process.env.NODE_ENV}`,
})

const config: GatsbyConfig = {
  siteMetadata: {
    title: `Hypertune Gatsby Demo`,
    siteUrl: `https://www.yourdomain.tld`,
  },
  graphqlTypegen: true,
  plugins: [],
}

export default config

4. Update .babelrc

First install the babel-preset-gatsby package as a devDependency:

npm

npm install -D babel-preset-gatsby

yarn

yarn add -D babel-preset-gatsby

pnpm

pnpm add -D babel-preset-gatsby

Then create a .babelrc at the root of your project:

.babelrc

{
  "presets": [
    [
      "babel-preset-gatsby",
      {
        "targets": {
          "browsers": [">0.25%", "not dead"]
        },
        "exclude": ["@babel/plugin-transform-classes"]
      }
    ]
  ]
}

5. Generate the client

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

npm

npx hypertune

yarn

yarn hypertune

pnpm

pnpm hypertune

6. Use the client

Add a new file called getHypertune.ts that creates and exports a getHypertune function:

lib/getHypertune.ts

import { createSourceForServerOnly } from '../generated/hypertune'

const hypertuneSource = createSourceForServerOnly({
  token: process.env.GATSBY_HYPERTUNE_TOKEN!,
})

export default async function getHypertune() {
  await hypertuneSource.initIfNeeded() // Check for flag updates

  return hypertuneSource.root({
    args: {
      context: {
        environment:
          process.env.NODE_ENV === 'development'
            ? 'development'
            : 'production',
        user: {
          id: 'e23cc9a8-0287-40aa-8500-6802df91e56a',
          name: 'Example User',
          email: '[e-mail]',
        },
      },
    },
  })
}

Server-side Rendering

To access flags in getServerData during Server-side Rendering (SSR), use the getHypertune function:

src/pages/ssr.tsx

import { GetServerData } from 'gatsby'
import * as React from 'react'
import getHypertune from '../lib/getHypertune'

type ServerData = { exampleFlag: boolean }

export const getServerData: GetServerData<
  ServerData
> = async () => {
  const hypertune = await getHypertune()

  const exampleFlag = hypertune.exampleFlag({ fallback: false })

  return { props: { exampleFlag } }
}

export default function Page({
  serverData,
}: {
  serverData: ServerData
}) {
  return <div>Example Flag: {serverData.exampleFlag}</div>
}

Client-side Rendering

To access flags in the browser during Client-side Rendering (CSR), first create a new <AppHypertuneProvider> component that wraps the generated <HypertuneProvider> component:

components/AppHypertuneProvider.tsx

import * as React from 'react'
import { HypertuneProvider } from '../generated/hypertune.react'

export default function AppHypertuneProvider({
  children,
}: {
  children: React.ReactNode
}) {
  return (
    <HypertuneProvider
      createSourceOptions={{
        token: process.env.GATSBY_HYPERTUNE_TOKEN!,
      }}
      rootArgs={{
        context: {
          environment:
            process.env.NODE_ENV === 'development'
              ? 'development'
              : 'production',
          user: {
            id: 'e23cc9a8-0287-40aa-8500-6802df91e56a',
            name: 'Example User',
            email: '[e-mail]',
          },
        },
      }}
    >
      {children}
    </HypertuneProvider>
  )
}

Then wrap your app with the <AppHypertuneProvider> component in both gatsby-browser.tsx and gatsby-ssr.tsx:

gatsby-ssr.tsx

import * as React from 'react'
import AppHypertuneProvider from './src/components/AppHypertuneProvider'
import type { GatsbyBrowser } from 'gatsby'

export const wrapRootElement: GatsbyBrowser['wrapRootElement'] =
  ({ element }) => {
    return <AppHypertuneProvider>{element}</AppHypertuneProvider>
  }

Then use the generated useHypertune hook:

src/components/ClientComponent.tsx

import * as React from 'react'
import { useHypertune } from '../generated/hypertune.react'

export default function ClientComponent() {
  const hypertune = useHypertune()

  const exampleFlag = hypertune.exampleFlag({ fallback: false })

  return <div>Example Flag: {String(exampleFlag)}</div>
}

If you access a flag immediately after your app loads, you'll get your hardcoded fallback value if the SDK hasn't initialized from Hypertune Edge yet. This can result in layout shift or a flicker if the flag value changes when the SDK initializes.

To avoid this, wrap your page with the generated <HypertuneHydrator> and <HypertuneRootProvider> components, passing them dehydratedState and rootArgs from the server:

src/pages/csr.tsx

import { GetServerData } from 'gatsby'
import * as React from 'react'
import ClientComponent from '../components/ClientComponent'
import {
  DehydratedState,
  RootArgs,
} from '../generated/hypertune'
import {
  HypertuneHydrator,
  HypertuneRootProvider,
} from '../generated/hypertune.react'
import getHypertune from '../lib/getHypertune'

type ServerData = {
  dehydratedState: DehydratedState | null
  rootArgs: RootArgs
}

export const getServerData: GetServerData<
  ServerData
> = async () => {
  const hypertune = await getHypertune()

  const dehydratedState = hypertune.dehydrate()
  const rootArgs = hypertune.getRootArgs()

  return {
    props: { dehydratedState, rootArgs },
  }
}

export default function Page({
  serverData,
}: {
  serverData: ServerData
}) {
  const { dehydratedState, rootArgs } = serverData

  return (
    <HypertuneHydrator dehydratedState={dehydratedState}>
      <HypertuneRootProvider rootArgs={rootArgs}>
        <ClientComponent />
      </HypertuneRootProvider>
    </HypertuneHydrator>
  )
}

If you have a Content Security Policy, add the following to your connect-src directive: https://edge.hypertune.com https://gcp.fasthorse.workers.dev. This enables reporting of flag evaluations, experiment exposures, and analytics events.

Functions

To access flags in Gatsby Functions, use the getHypertune function:

src/api/hello.ts

import {
  GatsbyFunctionRequest,
  GatsbyFunctionResponse,
} from 'gatsby'
import getHypertune from '../lib/getHypertune'

export default async function handler(
  req: GatsbyFunctionRequest,
  res: GatsbyFunctionResponse
) {
  const hypertune = await getHypertune()

  const exampleFlag = hypertune.exampleFlag({ fallback: false })

  res.send({ exampleFlag })
}

7. (Optional) Add the Hypertune Toolbar

The Hypertune Toolbar lets you view and override feature flags directly in your frontend. Follow the guide to add it to your app.

8. (Optional) Include a build-time snapshot

To improve reliability, you can include a snapshot of your flag logic in the generated client at build time. The SDK will instantly initialize from the snapshot first before fetching the latest flag logic from Hypertune Edge.

Add the following environment variable to your .env file:

HYPERTUNE_INCLUDE_INIT_DATA=true

Then regenerate the client.

You can keep the snapshot fresh by setting up a webhook to regenerate the client on every Hypertune commit. In this case, you don't need to initialize from Hypertune Edge at all, eliminating network latency and bandwidth, improving both performance and efficiency.

Next steps

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.