React SDK reference

This reference guide documents all of the methods available in our client-side React SDK, and explains in detail how these methods work. If you want to dig even deeper, our SDKs are open source — head to the React SDK code in our JavaScript SDK GitHub repository. The online API docs contain the programmatic definitions of every type and method. You can also clone and run a sample application using this SDK.

If you want to use LaunchDarkly in a Gatsby application, we have a Gatsby plugin.

Getting started

Building on top of our Getting Started guide guide, the following steps will get you started with using the LaunchDarkly SDK in your React code.

You can use either npm or yarn to install the React SDK:

1npm i --save launchdarkly-react-client-sdk
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Once the dependency is installed, you'll want to initialize the React SDK. To do this, you need your environment's client-side ID (available on your account settings page). Client-side IDs are not secret. You can expose them in your client-side code with no risk.

There are two ways you can initialize the React SDK. The first is using the asyncWithLDProvider function. The second is using the withLDProvider function. Both rely on React's Context API to make it easy for you to access your flags from any level of your component hierarchy. Both functions accept a ProviderConfig object used to configure the React SDK. Continue reading below for more information about these functions.

asyncWithLDProvider

The asyncWithLDProvider function initializes the React SDK and returns a provider which is a React component. It is an async function.

1import { asyncWithLDProvider } from 'launchdarkly-react-client-sdk';
2
3(async () => {
4  const LDProvider = await asyncWithLDProvider({
5    clientSideID: 'your-client-side-id',
6    user: {
7      "key": "aa0ceb",
8      "name": "Grace Hopper",
9      "email": "gracehopper@example.com"
10    },
11    options: { /* ... */ }
12  });
13
14  render(
15    <LDProvider>
16      <YourApp />
17    </LDProvider>,
18    document.getElementById('reactDiv'),
19  );
20})();
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Once initialization is complete, your flags and the ldClient will be available at the start of your React app lifecycle. This will ensure your app does not flicker due to flag changes at startup time.

withLDProvider

The withLDProvider function initializes the React SDK and wraps your root component in a Context.Provider:

1import { withLDProvider } from 'launchdarkly-react-client-sdk';
2
3export default withLDProvider({ 
4  clientSideID: 'your-client-side-id',
5  user: {
6    "key": "aa0ceb",
7    "name": "Grace Hopper",
8    "email": "gracehopper@example.com"
9  },
10  options: { /* ... */ }
11})(YourApp);
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Customize your client from the options field. To learn more, read the JavaScript SDK reference.

Note that the React SDK automatically subscribes to flag change events; this is unlike the JavaScript SDK reference where customers need to opt in to event listening. Consequently, in the React SDK, streaming mode is enabled by default. To disable streaming mode, specify a streaming: false attribute in your options object.

withLDConsumer

The return value of withLDConsumer is a wrapper function that takes your component and returns a React component injected with flags & ldClient as props.

1import { withLDConsumer } from 'launchdarkly-react-client-sdk';
2
3const Home = ({ flags, ldClient /*, ...otherProps */ }) => {
4  // You can call any of the methods from the JavaScript SDK
5  // ldClient.identify({...})
6  
7  return flags.devTestFlag ? <div>Flag on</div> : <div>Flag off</div>;
8};
9
10export default withLDConsumer()(Home);
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Configuring the React SDK

The ProviderConfig object is used to configure the React SDK. The only mandatory property is the client-side id. All other properties are optional.

• clientSideID: This is your project and environment specific client-side id. This property is mandatory.

• user: A LaunchDarkly user object. This property is optional.

• options: LaunchDarkly JavaScript SDK initialization options. This property is optional.

• reactOptions: This property is specific to the React SDK. You can use this option to disable automatic camel casing of flag keys when using the React SDK. This property is optional.

• deferInitialization: This property allows SDK initialization to be deferred until the user property is defined.

  By deferring SDK initialization, the customer is deferring all steps which take place as part of SDK initialization, including reading flag values from local storage and sending the SDK's ready event.

  The one exception to this rule is that the SDK will continue to load bootstrapped flag values as long as the bootstrapped values are provided as a map of flag keys and values. As mentioned above, if indicated that the SDK should bootstrap flags from local storage, this will not happen until the SDK initializes.

• flags: If specified, the React SDK will only subscribe for updates to these flags. The React SDK will subscribe to all flags when this property is unspecified. This property is optional.

  The flags property should be specified as a map of flag keys and values. The flag keys must be in their original form (as known to LaunchDarkly) rather than in their camel-cased form. Each flag's value will be passed along to the resulting JS SDK variation invocation and used as the flag's default value in the case of an error.

The following is an example ProviderConfig object including each of the above properties:

1{
2  clientSideID: "your-client-side-id",
3  user: {
4    key: "aa0ceb",
5    name: "Grace Hopper",
6    email: "gracehopper@example.com"
7  },
8  options: {
9    bootstrap: "localStorage"
10  },
11  reactOptions: { 
12    useCamelCaseFlagKeys: false
13  },
14  deferInitialization: false,
15  flags: {
16    "my-bool-flag": true,
17    "my-int-flag": 5
18  }
19}
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Hooks

The React SDK offers two custom hooks which you can use as an alternative to withLDConsumer: useFlags and useLDClient.

useFlags is a custom hook which returns all feature flags. It uses the useContext primitive to access the LaunchDarkly context set up by asyncWithLDProvider or withLDProvider. You will still need to use the asyncWithLDProvider or the withLDProvider higher-order component at the root of your application to initialize the React SDK and populate the context with LDClient and your flags.

useLDClient is the second custom hook which returns the underlying LaunchDarkly JavaScript SDK client object. Like the useFlags custom hook, useLDClient also uses the useContext primitive to access the LaunchDarkly context set up by asyncWithLDProvider or withLDProvider. You will still need to use the asyncWithLDProvider or the withLDProvider higher-order component to initialize the React SDK to use this custom hook.

1import React from 'react';
2import { useFlags, useLDClient } from 'launchdarkly-react-client-sdk';
3
4const HooksDemo = () => {
5  const { devTestFlag } = useFlags();
6  const ldClient = useLDClient();
7  
8  const onLoginSuccessful = () => ldClient.identify({ key: 'aa0ceb' });
9
10  return (
11    <div>{devTestFlag ? 'Flag on' : 'Flag off'}</div>
12  );
13};
14
15export default HooksDemo;
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Users

All user-related functionality provided by the JavaScript SDK is equally accessible in the React SDK. Refer to the users, private user attributes, and anonymous users sections of the JavaScript SDK reference guide for more information.

Unlike the JavaScript SDK, where a user object is required for initialization, the React SDK does not require a user object. If one is not specified, the React SDK will proceed with an anonymous user by default.

Flag keys

LaunchDarkly primarily identifies feature flags by a key which must only contain alphanumeric characters, dots (.), underscores (_), and dashes (-). These keys are used across all of LaunchDarkly's APIs as well as in the SDKs to identify flags.

However, keys in this format are slightly inconvenient to access in JavaScript and React as they cannot be accessed with the dot notation. As a result, the React SDK automatically camel-cases all flag keys. A flag with key dev-flag-test would be accessible as flags.devFlagTest.

Automatically camel-casing flag keys poses some problems, though:

1. It is possible to induce a key collision if there are multiple LaunchDarkly flag keys which resolve to the same camel-cased key. For example, dev-flag-test and dev.flag.test would be considered unique keys on LaunchDarkly yet the React SDK would consider them to have the same camel-cased keys.
2. Our Code references tool expects your source code to reference the exact key, not a camel-cased equivalent, so the tool does not support detecting references of keys that were automatically camel-cased.
3. As the camel-casing functionality is implemented in the React SDK instead of in the underlying JavaScript SDK, the underlying ldClient object and functionality provided by the JavaScript SDK reflect flag keys in their original format. Only React-specific contexts such as your injected props are camel-cased.

To disable the SDK's automatic camel-casing feature, you can provide asyncWithLDProvider or withLDProvider with the reactOptions.useCamelCaseFlagKeys property as shown in the following example. This is supported in versions 2.13.0 and later of the React SDK.

1export default withLDProvider({ 
2  clientSideID: 'your-client-side-id',
3  reactOptions: { 
4    useCamelCaseFlagKeys: false
5  }
6})(App);
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With this configuration option in place, you would now access your dev-flag-test flag using bracket notation. For example, flag['dev-flag-test'].

Example App

Check the example for a fully working single page app with react and react-router. You'll need to enter your clientSideId in the client root app file and create a flag with key dev-test-flag in your dashboard before running the example.