React SDK

React client side library for Reflag.com

Reflag supports flag toggling, tracking flag usage, requesting feedback on features, and remotely configuring flags.

The Reflag React SDK comes with a built-in toolbar which appears on localhost by default.

Install

Install via npm:

npm i @reflag/react-sdk

Get started

1. Add the ReflagProvider context provider

Add the ReflagProvider context provider to your application:

Example:

import { ReflagProvider } from "@reflag/react-sdk";

<ReflagProvider
  publishableKey="{YOUR_PUBLISHABLE_KEY}"
  context={{
    company: { id: "acme_inc", plan: "pro" },
    user: { id: "john doe" },
  }}
  loadingComponent={<Loading />}
>
  {/* children here are shown when loading finishes or immediately if no `loadingComponent` is given */}
</ReflagProvider>;

2. Create a new flag and set up type safety

Install the Reflag CLI:

npm i --save-dev @reflag/cli

Run npx reflag new to create your first flag! On the first run, it will sign into Reflag and set up type generation for your project:

❯ npx reflag new
Opened web browser to facilitate login: https://app.reflag.com/api/oauth/cli/authorize

Welcome to ◪ Reflag!

? Where should we generate the types? gen/flags.d.ts
? What is the output format? react
✔ Configuration created at reflag.config.json.

Creating flag for app Slick app.
? New flag name: Huddle
? New flag key: huddle
✔ Created flag Huddle with key huddle (https://app.reflag.com/features/huddles)
✔ Generated react types in gen/flags.d.ts.

[!Note] By default, types will be generated in gen/flags.d.ts. The default tsconfig.json file includes this file by default, but if your tsconfig.json is different, make sure the file is covered in the include property.

3. Use useFlag(<flagKey>) to get flag status

Using the useFlag hook from your components lets you toggle flags on/off and track flag usage:

Example:

function StartHuddleButton() {
  const {
    isEnabled, // boolean indicating if the flag is enabled
    track, // track usage of the flag
  } = useFlag("huddle");

  if (!isEnabled) {
    return null;
  }

  return <button onClick={track}>Start huddle!</button>;
}

useFlag can help you do much more. See a full example for useFlag see below.

Setting context

Reflag determines which flags are active for a given user, company, or other context. You can pass these to the ReflagProvider using the context prop.

Using the context prop

<ReflagProvider
  publishableKey={YOUR_PUBLISHABLE_KEY}
  context={{
    user: { id: "user_123", name: "John Doe", email: "[email protected]" },
    company: { id: "company_123", name: "Acme, Inc" },
    other: { source: "web" },
  }}
>
  <LoadingReflag>
    {/* children here are shown when loading finishes */}
  </LoadingReflag>
</ReflagProvider>

Legacy individual props (deprecated)

For backward compatibility, you can still use individual props, but these are deprecated and will be removed in the next major version:

<ReflagProvider
  publishableKey={YOUR_PUBLISHABLE_KEY}
  user={{ id: "user_123", name: "John Doe", email: "[email protected]" }}
  company={{ id: "company_123", name: "Acme, Inc" }}
  otherContext={{ source: "web" }}
>
  <LoadingReflag>
    {/* children here are shown when loading finishes */}
  </LoadingReflag>
</ReflagProvider>

[!Important] The user, company, and otherContext props are deprecated. Use the context prop instead, which provides the same functionality in a more structured way.

Context requirements

If you supply user or company objects, they must include at least the id property otherwise they will be ignored in their entirety. In addition to the id, you must also supply anything additional that you want to be able to evaluate flag targeting rules against. Attributes which are not properties of the user or company can be supplied using the other property.

Attributes cannot be nested (multiple levels) and must be either strings, numbers or booleans. A number of special attributes exist:

• name -- display name for user/company,

• email -- the email of the user,

• avatar -- the URL for user/company avatar image.

To retrieve flags along with their targeting information, use useFlag(key: string) hook (described in a section below).

Note that accessing isEnabled on the object returned by useFlag() automatically generates a check event.

Remote config

Remote config is a dynamic and flexible approach to configuring flag behavior outside of your app – without needing to re-deploy it.

Similar to isEnabled, each flag accessed using the useFlag() hook, has a config property. This configuration is managed from within Reflag. It is managed similar to the way access to flags is managed, but instead of the binary isEnabled you can have multiple configuration values which are given to different user/companies.

Get started with Remote config

1. Update your flag definitions:

import "@reflag/react-sdk";

// Define your flags by extending the `Flags` interface in @reflag/react-sdk
declare module "@reflag/react-sdk" {
  interface Flags {
    huddle: {
      // change from `boolean` to an object which sets
      // a type for the remote config for `questionnaire`
      maxTokens: number;
      model: string;
    };
  }
}

const {
  isEnabled,
  config: { key, payload },
} = useFlag("huddles");

// isEnabled: true,
// key: "gpt-3.5",
// payload: { maxTokens: 10000, model: "gpt-3.5-beta1" }

key is mandatory for a config, but if a flag has no config or no config value was matched against the context, the key will be undefined. Make sure to check against this case when trying to use the configuration in your application. payload is an optional JSON value for arbitrary configuration needs.

Note that, similar to isEnabled, accessing config on the object returned by useFlag() automatically generates a check event.

Toolbar

The Reflag Toolbar is great for toggling flags on/off for yourself to ensure that everything works both when a flag is on and when it's off.

The toolbar will automatically appear on localhost. However, it can also be incredibly useful in production. You have full control over when it appears through the toolbar configuration option passed to the ReflagProvider.

You can pass a simple boolean to force the toolbar to appear/disappear:

<ReflagProvider
  ...
  // show the toolbar even in production if the user is an internal/admin user
  toolbar={user?.isInternal}
  ...
});

Server-side rendering and bootstrapping

For server-side rendered applications, you can eliminate the initial network request by bootstrapping the client with pre-fetched flag data using the ReflagBootstrappedProvider.

Using ReflagBootstrappedProvider

The <ReflagBootstrappedProvider> component is a specialized version of ReflagProvider designed for server-side rendering and preloaded flag scenarios. Instead of fetching flags on initialization, it uses pre-fetched flags, resulting in faster initial page loads and better SSR compatibility.

import { useState, useEffect } from "react";
import { BootstrappedFlags } from "@reflag/react-sdk";

interface BootstrapData {
  user: User;
  flags: BootstrappedFlags;
}

function useBootstrap() {
  const [data, setData] = useState<BootstrapData | null>(null);

  useEffect(() => {
    fetch("/bootstrap")
      .then((res) => res.json())
      .then(setData);
  }, []);

  return data;
}

// Usage in your app
function App() {
  const { user, flags } = useBootstrap();

  return (
    <AuthProvider user={user}>
      <ReflagBootstrappedProvider
        publishableKey="your-publishable-key"
        flags={flags}
      >
        <Router />
      </ReflagBootstrappedProvider>
    </AuthProvider>
  );
}

Server-side endpoint setup

Create an endpoint that provides bootstrap data to your client application:

// server.js or your Express app
import { ReflagClient as ReflagNodeClient } from "@reflag/node-sdk";

const reflagClient = new ReflagNodeClient({
  secretKey: process.env.REFLAG_SECRET_KEY,
});
await reflagClient.initialize();

app.get("/bootstrap", (req, res) => {
  const user = getUser(req); // Get user from your auth system
  const company = getCompany(req); // Get company from your auth system

  const flags = reflagClient.getFlagsForBootstrap({
    user: { id: "user123", name: "John Doe", email: "[email protected]" },
    company: { id: "company456", name: "Acme Inc", plan: "enterprise" },
    other: { source: "web" },
  });

  res.status(200).json({
    user,
    flags,
  });
});

Next.js Page Router SSR example

For Next.js applications using server-side rendering, you can pre-fetch flags in getServerSideProps:

// pages/index.tsx
import { GetServerSideProps } from "next";
import { ReflagClient as ReflagNodeClient } from "@reflag/node-sdk";
import { ReflagBootstrappedProvider, BootstrappedFlags, useFlag } from "@reflag/react-sdk";

interface PageProps {
  bootstrapData: BootstrappedFlags;
}

export const getServerSideProps: GetServerSideProps = async (context) => {
  const serverClient = new ReflagNodeClient({
    secretKey: process.env.REFLAG_SECRET_KEY
  });
  await serverClient.initialize();

  const user = await getUserFromSession(context.req);
  const company = await getCompanyFromUser(user);

  const bootstrapData = serverClient.getFlagsForBootstrap({
    user: { id: "user123", name: "John Doe", email: "[email protected]" },
    company: { id: "company456", name: "Acme Inc", plan: "enterprise" },
    other: { page: "homepage" }
  });

  return { props: { bootstrapData } };
};

export default function HomePage({ bootstrapData }: PageProps) {
  return (
    <ReflagBootstrappedProvider
      publishableKey={process.env.NEXT_PUBLIC_REFLAG_PUBLISHABLE_KEY}
      flags={bootstrapData}
    >
      <HuddleFeature />
    </ReflagBootstrappedProvider>
  );
}

function HuddleFeature() {
  const { isEnabled, track, config } = useFlag("huddle");

  if (!isEnabled) return null;

  return (
    <div>
      <h2>Start a Huddle</h2>
      <p>Max participants: {config.payload?.maxParticipants ?? 10}</p>
      <p>Video quality: {config.payload?.videoQuality ?? "standard"}</p>
      <button onClick={track}>Start Huddle</button>
    </div>
  );
}

This approach eliminates loading states and improves performance by avoiding the initial flags API call.

Next.js App Router example

For Next.js applications using the App Router (Next.js 13+), you can pre-fetch flags in Server Components and pass them to client components:

// app/layout.tsx (Server Component)
import { ReflagClient as ReflagNodeClient } from "@reflag/node-sdk";
import { ClientProviders } from "./providers";

async function getBootstrapData() {
  const serverClient = new ReflagNodeClient({
    secretKey: process.env.REFLAG_SECRET_KEY!
  });
  await serverClient.initialize();

  // In a real app, you'd get user/company from your auth system
  const bootstrapData = serverClient.getFlagsForBootstrap({
    user: { id: "user123", name: "John Doe", email: "[email protected]" },
    company: { id: "company456", name: "Acme Inc", plan: "enterprise" },
    other: { source: "web" }
  });

  return bootstrapData;
}

export default async function RootLayout({
  children,
}: {
  children: React.ReactNode;
}) {
  const bootstrapData = await getBootstrapData();

  return (
    <html lang="en">
      <body>
        <ClientProviders bootstrapData={bootstrapData}>
          {children}
        </ClientProviders>
      </body>
    </html>
  );
}

// app/providers.tsx (Client Component)
"use client";

import { ReflagBootstrappedProvider, BootstrappedFlags } from "@reflag/react-sdk";

interface ClientProvidersProps {
  children: React.ReactNode;
  bootstrapData: BootstrappedFlags;
}

export function ClientProviders({ children, bootstrapData }: ClientProvidersProps) {
  return (
    <ReflagBootstrappedProvider
      publishableKey={process.env.NEXT_PUBLIC_REFLAG_PUBLISHABLE_KEY!}
      flags={bootstrapData}
    >
      {children}
    </ReflagBootstrappedProvider>
  );
}

// app/page.tsx (Server Component)
import { HuddleFeature } from "./huddle-feature";

export default function HomePage() {
  return (
    <main>
      <h1>My App</h1>
      <HuddleFeature />
    </main>
  );
}

// app/huddle-feature.tsx (Client Component)
"use client";

import { useFlag } from "@reflag/react-sdk";

export function HuddleFeature() {
  const { isEnabled, track, config } = useFlag("huddle");

  if (!isEnabled) return null;

  return (
    <div>
      <h2>Start a Huddle</h2>
      <p>Max participants: {config.payload?.maxParticipants ?? 10}</p>
      <p>Video quality: {config.payload?.videoQuality ?? "standard"}</p>
      <button onClick={track}>Start Huddle</button>
    </div>
  );
}

This App Router approach leverages Server Components for server-side flag fetching while using Client Components only where React state and hooks are needed.

<ReflagClientProvider> component

The <ReflagClientProvider> is a lower-level component that accepts a pre-initialized ReflagClient instance. This is useful for advanced use cases where you need full control over client initialization or want to share a client instance across multiple parts of your application.

Usage

import { ReflagClient } from "@reflag/browser-sdk";
import { ReflagClientProvider } from "@reflag/react-sdk";

// Initialize the client yourself
const client = new ReflagClient({
  publishableKey: "your-publishable-key",
  user: { id: "user123", name: "John Doe" },
  company: { id: "company456", name: "Acme Inc" },
  // ... other configuration options
});

// Initialize the client
await client.initialize();

function App() {
  return (
    <ReflagClientProvider client={client} loadingComponent={<Loading />}>
      <Router />
    </ReflagClientProvider>
  );
}

Props

The ReflagClientProvider accepts the following props:

• client: A pre-initialized ReflagClient instance

• loadingComponent: Optional React component to show while the client is initializing (same as ReflagProvider)

[!Note] Most applications should use ReflagProvider or ReflagBootstrappedProvider instead of ReflagClientProvider. Only use this component when you need the advanced control it provides.

<ReflagProvider> component

The <ReflagProvider> initializes the Reflag SDK, fetches flags and starts listening for automated feedback survey events. The component can be configured using a number of props:

• publishableKey is used to connect the provider to an environment on Reflag. Find your publishableKey under environment settings in Reflag,

• context (recommended): An object containing user, company, and other properties that make up the evaluation context used to determine if a flag is enabled or not. company and user contexts are automatically transmitted to Reflag servers so the Reflag app can show you which companies have access to which flags etc.

• company, user and other (deprecated): Individual props for context. These are deprecated in favor of the context prop and will be removed in the next major version.

  [!Note] If you specify company and/or user they must have at least the id property, otherwise they will be ignored in their entirety. You should also supply anything additional you want to be able to evaluate flag targeting against,

• fallbackFlags: A list of strings which specify which flags to consider enabled if the SDK is unable to fetch flags. Can be provided in two formats:

  // Simple array of flag keys
  fallbackFlags={["flag1", "flag2"]}
  
  // Or with configuration overrides
  fallbackFlags: {
      "flag1": true,  // just enable the flag
      "flag2": {      // enable with configuration
        key: "variant-a",
        payload: {
          limit: 100,
          mode: "test"
        }
      }
  }

• timeoutMs: Timeout in milliseconds when fetching flags from the server.

• staleWhileRevalidate: If set to true, stale flags will be returned while refetching flags in the background.

• expireTimeMs: If set, flags will be cached between page loads for this duration (in milliseconds).

• staleTimeMs: Maximum time (in milliseconds) that stale flags will be returned if staleWhileRevalidate is true and new flags cannot be fetched.

• offline: Provide this option when testing or in local development environments to avoid contacting Reflag servers.

• loadingComponent lets you specify an React component to be rendered instead of the children while the Reflag provider is initializing. If you want more control over loading screens, useFlag() and useIsLoading returns isLoading which you can use to customize the loading experience.

• enableTracking: Set to false to stop sending tracking events and user/company updates to Reflag. Useful when you're impersonating a user (defaults to true),

• apiBaseUrl: Optional base URL for the Reflag API. Use this to override the default API endpoint,

• appBaseUrl: Optional base URL for the Reflag application. Use this to override the default app URL,

• sseBaseUrl: Optional base URL for Server-Sent Events. Use this to override the default SSE endpoint,

• debug: Set to true to enable debug logging to the console,

• toolbar: Optional configuration for the Reflag toolbar,

• feedback: Optional configuration for feedback collection

<ReflagBootstrappedProvider> component

The <ReflagBootstrappedProvider> is a specialized version of the ReflagProvider that uses pre-fetched flag data instead of making network requests during initialization. This is ideal for server-side rendering scenarios.

The component accepts the following props:

• flags: Pre-fetched flags data of type BootstrappedFlags obtained from the Node SDK's getFlagsForBootstrap() method. This contains both the context (user, company, other) and the flags data.

• All other props available in ReflagProvider are supported except context, user, company, and other (which are extracted from flags.context).

Example:

import {
  ReflagBootstrappedProvider,
  BootstrappedFlags,
} from "@reflag/react-sdk";

interface AppProps {
  bootstrapData: BootstrappedFlags;
}

function App({ bootstrapData }: AppProps) {
  return (
    <ReflagBootstrappedProvider
      publishableKey="your-publishable-key"
      flags={bootstrapData}
      loadingComponent={<Loading />}
      debug={process.env.NODE_ENV === "development"}
    >
      <Router />
    </ReflagBootstrappedProvider>
  );
}

[!Note] When using ReflagBootstrappedProvider, the context (user, company, and other) is extracted from the flags.context property and doesn't need to be passed separately.

Hooks

useFlag()

Returns the state of a given flag for the current context. The hook provides type-safe access to flags and their configurations.

import { useFlag } from "@reflag/react-sdk";
import { Loading } from "./Loading";

function StartHuddleButton() {
  const {
    isLoading, // true while flags are being loaded
    isEnabled, // boolean indicating if the flag is enabled
    config: {
      // flag configuration
      key, // string identifier for the config variant
      payload, // type-safe configuration object
    },
    track, // function to track flag usage
    requestFeedback, // function to request feedback for this flag
  } = useFlag("huddle");

  if (isLoading) {
    return <Loading />;
  }

  if (!isEnabled) {
    return null;
  }

  return (
    <>
      <button onClick={track}>Start huddle!</button>
      <button
        onClick={(e) =>
          requestFeedback({
            title: payload?.question ?? "How do you like the Huddles feature?",
            position: {
              type: "POPOVER",
              anchor: e.currentTarget as HTMLElement,
            },
          })
        }
      >
        Give feedback!
      </button>
    </>
  );
}

useTrack()

useTrack() lets you send custom events to Reflag. Use this whenever a user uses a feature. These events can be used to analyze feature usage in Reflag.

import { useTrack } from "@reflag/react-sdk";

function StartHuddle() {
  const { track } = useTrack();
  <div>
    <button onClick={() => track("Huddle Started", { huddleType: "voice" })}>
      Start voice huddle!
    </button>
  </div>;
}

useRequestFeedback()

useRequestFeedback() returns a function that lets you open up a dialog to ask for feedback on a specific feature. This is useful for collecting targeted feedback about specific features as part of roll out. See Automated Feedback Surveys for how to do this automatically, without code.

When using the useRequestFeedback you must pass the flag key to requestFeedback. The example below shows how to use position to ensure the popover appears next to the "Give feedback!" button.

import { useRequestFeedback } from "@reflag/react-sdk";

function FeedbackButton() {
  const requestFeedback = useRequestFeedback();
  return (
    <button
      onClick={(e) =>
        requestFeedback({
          flagKey: "huddle-flag",
          title: "How satisfied are you with file uploads?",
          position: {
            type: "POPOVER",
            anchor: e.currentTarget as HTMLElement,
          },
          // Optional custom styling
          style: {
            theme: "light",
            primaryColor: "#007AFF",
          },
        })
      }
    >
      Give feedback!
    </button>
  );
}

See the Feedback Documentation for more information on requestFeedback options.

useSendFeedback()

Returns a function that lets you send feedback to Reflag. This is useful if you've manually collected feedback through your own UI and want to send it to Reflag.

import { useSendFeedback } from "@reflag/react-sdk";

function CustomFeedbackForm() {
  const sendFeedback = useSendFeedback();

  const handleSubmit = async (data: FormData) => {
    await sendFeedback({
      flagKey: "reflag-flag-key",
      score: parseInt(data.get("score") as string),
      comment: data.get("comment") as string,
    });
  };

  return <form onSubmit={handleSubmit}>...</form>;
}

useUpdateUser(), useUpdateCompany() and useUpdateOtherContext()

These hooks return functions that let you update the attributes for the currently set user, company, or other context. Updates to user/company are stored remotely and affect flag targeting, while "other" context updates only affect the current session.

import {
  useUpdateUser,
  useUpdateCompany,
  useUpdateOtherContext,
} from "@reflag/react-sdk";

function FlagOptIn() {
  const updateUser = useUpdateUser();
  const updateCompany = useUpdateCompany();
  const updateOtherContext = useUpdateOtherContext();

  const handleUserUpdate = async () => {
    await updateUser({
      role: "admin",
      betaFlags: "enabled",
    });
  };

  const handleCompanyUpdate = async () => {
    await updateCompany({
      plan: "enterprise",
      employees: 500,
    });
  };

  const handleContextUpdate = async () => {
    await updateOtherContext({
      currentWorkspace: "workspace-123",
      theme: "dark",
    });
  };

  return (
    <div>
      <button onClick={handleUserUpdate}>Update User</button>
      <button onClick={handleCompanyUpdate}>Update Company</button>
      <button onClick={handleContextUpdate}>Update Context</button>
    </div>
  );
}

useClient()

Returns the ReflagClient used by the ReflagProvider. The client offers more functionality that is not directly accessible thorough the other hooks.

import { useClient } from "@reflag/react-sdk";

function LoggingWrapper({ children }: { children: ReactNode }) {
  const client = useClient();

  console.log(client.getContext());

  return children;
}

useIsLoading()

Returns the loading state of the flags in the ReflagClient. Initially, the value will be true if no bootstrap flags have been provided and the client has not be initialized.

import { useIsLoading } from "@reflag/react-sdk";
import { Spinner } from "./Spinner";

function LoadingWrapper({ children }: { children: ReactNode }) {
  const isLoading = useIsLoading();

  if (isLoading) {
    return <Spinner />;
  }

  return children;
}

useOnEvent()

Attach a callback handler to client events to act on changes. It automatically disposes itself on unmount.

import { useOnEvent } from "@reflag/react-sdk";

function LoggingWrapper({ children }: { children: ReactNode }) {
  useOnEvent("flagsUpdated", (newFlags) => {
    console.log(newFlags);
  });

  return children;
}

Migrating from Bucket SDK

If you have been using the Bucket SDKs, the following list will help you migrate to Reflag SDK:

• Bucket* classes, and types have been renamed to Reflag* (e.g. BucketClient is now ReflagClient)

• Feature* classes, and types have been renamed to Flag* (e.g. Feature is now Flag, RawFeatures is now RawFlags)

• When using strongly-typed flags, the new Flags interface replaced Features interface

• All methods that contained feature in the name have been renamed to use the flag terminology (e.g. getFeature is getFlag)

• The fallbackFeatures property in client constructor and configuration files has been renamed to fallbackFlags

• featureKey has been renamed to flagKey in all methods that accepts that argument

• The SDKs will not emit evaluate and evaluate-config events anymore

• The new cookies that are stored in the client's browser are now reflag-* prefixed instead of bucket-*

• The featuresUpdated hook has been renamed to flagsUpdated

• The checkIsEnabled and checkConfig hooks have been removed, use check from now on

To ease in transition to Reflag SDK, some of the old methods have been preserved as aliases to the new methods:

• getFeature method is an alias for getFlag

• getFeatures method is an alias for getFlags

• useFeature method is an alias for useFlag

• featuresUpdated hook is an alias for flagsUpdated

If you are running with strict Content Security Policies active on your website, you will need change them as follows:

• connect-src https://front.bucket.co to connect-src https://front.reflag.com

Content Security Policy (CSP)

See CSP for info on using Reflag React SDK with CSP

License

MIT License

Copyright (c) 2025 Bucket ApS