Version: Config V2

React SDK Reference

ConfigCat React SDK on GitHub

Getting started

1. Install package

npm i configcat-react

2. Import and initialize a `ConfigCatProvider` with your SDK Key

In most cases you should wrap your root component with ConfigCatProvider to access ConfigCat features in child components with Context API.

import React from 'react';
import { ConfigCatProvider } from 'configcat-react';

function App() {
  return (
    <ConfigCatProvider sdkKey="#YOUR_SDK_KEY#">
      {/* your application code */}
    </ConfigCatProvider>
  );
}

export default App;

3. Get your setting value

The React hooks (useFeatureFlag) way:

function ButtonComponent() {
  const { value: isAwesomeFeatureEnabled, loading } = useFeatureFlag(
    'isAwesomeFeatureEnabled',
    false,
  );

  return loading ? (
    <div>Loading...</div>
  ) : (
    <div>Feature flag value: {isAwesomeFeatureEnabled ? 'ON' : 'OFF'}</div>
  );
}

The React HOC (WithConfigCatClientProps) way:

class TestHOCComponent extends React.Component<
  WithConfigCatClientProps,
  { isAwesomeFeatureEnabled: boolean; loading: boolean }
> {
  constructor(props: WithConfigCatClientProps) {
    super(props);

    this.state = { isAwesomeFeatureEnabled: false, loading: true };
  }

  componentDidMount() {
    this.evaluateFeatureFlag();
  }

  componentDidUpdate(prevProps: any) {
    // To achieve hot reload on config JSON updates.
    if (prevProps?.lastUpdated !== this.props.lastUpdated) {
      this.evaluateFeatureFlag();
    }
  }

  evaluateFeatureFlag() {
    this.props
      .getValue('isAwesomeFeatureEnabled', false)
      .then((v: boolean) =>
        this.setState({ isAwesomeFeatureEnabled: v, loading: false }),
      );
  }

  render() {
    return loading ? (
      <div>Loading...</div>
    ) : (
      <div>
        Feature flag value: {this.state.isAwesomeFeatureEnabled ? 'ON' : 'OFF'}
      </div>
    );
  }
}

const ConfigCatTestHOCComponent = withConfigCatClient(TestHOCComponent);

Creating the ConfigCat Client

ConfigCat Client is responsible for:

managing the communication between your application and ConfigCat servers.
caching your setting values and feature flags.
serving values quickly in a failsafe way.

<ConfigCatProvider sdkKey="#YOUR_SDK_KEY#" pollingMode={PollingMode.AutoPoll} options={{ ... }}> initializes a client.

Attributes	Description	Default
`sdkKey`	REQUIRED. SDK Key to access your feature flags and configurations. Get it from ConfigCat Dashboard.	-
`pollingMode`	Optional. The polling mode to use to acquire the setting values from the ConfigCat servers. More about polling modes.	`PollingMode.AutoPoll`
`options`	Optional. The options object. See the table below.	-
`id`	Optional. Instructs the ConfigCat Client to use a specific `ConfigCatProvider` instead of the default one. Use it if you have multiple `ConfigCatProvider`s in your code. More about multiple providers.	`undefined` (none)

The available options depends on the chosen polling mode. However, there are some common options which can be set in the case of every polling mode:

Option Parameter	Description	Default
`logger`	Custom `IConfigCatLogger` implementation for tracing.	`ConfigCatConsoleLogger` (with WARN level)
`requestTimeoutMs`	The amount of milliseconds the SDK waits for a response from the ConfigCat servers before returning values from the cache.	30000
`baseUrl`	Sets the CDN base url (forward proxy, dedicated subscription) from where the SDK will download the config JSON.
`dataGovernance`	Describes the location of your feature flag and setting data within the ConfigCat CDN. This parameter needs to be in sync with your Data Governance preferences. More about Data Governance. Available options: `DataGovernance.Global`, `DataGovernance.EuOnly`.	`DataGovernance.Global`
`cache`	Custom `IConfigCatCache` implementation for caching the downloaded config.	`InMemoryConfigCache`
`flagOverrides`	Local feature flag & setting overrides. More about feature flag overrides.	-
`defaultUser`	Sets the default user. More about default user.	`undefined` (none)
`offline`	Determines whether the client should be initialized to offline mode. More about offline mode.	`false`

Options also include a property named setupHook, which you can use to subscribe to the hooks (events) at the time of initialization. More about hooks.

For example:

<ConfigCatProvider
  sdkKey="YOUR_SDK_KEY"
  pollingMode={PollingMode.AutoPoll}
  options={{
    setupHooks: (hooks) =>
      hooks.on('clientReady', () => console.log('Client is ready!')),
  }}
>
  ...
</ConfigCatProvider>

Acquire the ConfigCat instance

The SDK supports two ways to acquire the initialized ConfigCat instance:

Custom hook: useConfigCatClient() (from React v16.8)
Higher-order component: withConfigCatClient()

Anatomy of `useFeatureFlag()`

Parameters	Description
`key`	REQUIRED. Setting-specific key. Set on ConfigCat Dashboard for each setting.
`defaultValue`	REQUIRED. This value will be returned in case of an error.
`user`	Optional, User Object. Essential when using Targeting. Read more about Targeting.
`providerId`	Optional. Instructs the ConfigCat Client to use a specific `ConfigCatProvider` instead of the default one. Use it if you have multiple `ConfigCatProvider`s in your code. More about multiple providers.

function ButtonComponent() {
  const { value: isAwesomeFeatureEnabled, loading } = useFeatureFlag(
    'isAwesomeFeatureEnabled',
    false,
  );

  return loading ? (
    <div>Loading...</div>
  ) : (
    <div>Feature flag value: {isAwesomeFeatureEnabled ? 'ON' : 'OFF'}</div>
  );
}

caution

It is important to provide an argument for the defaultValue parameter that matches the type of the feature flag or setting you are evaluating. Please refer to the following table for the corresponding types.

Setting type mapping

Setting Kind	`typeof defaultValue`
On/Off Toggle	`boolean`
Text	`string`
Whole Number	`number`
Decimal Number	`number`

In addition to the types mentioned above, you also have the option to provide null or undefined for the defaultValue parameter regardless of the setting kind. However, if you do so, the type of value returned by the useFeatureFlag method will be

boolean | string | number | null when defaultValue is null or
boolean | string | number | undefined when defaultValue is undefined.

This is because in these cases the exact return type cannot be determined at compile-time as the TypeScript compiler has no information about the setting type.

It's important to note that providing any other type for the defaultValue parameter will result in a TypeError.

If you specify an allowed type but it mismatches the setting kind, an error message will be logged and defaultValue will be returned.

Anatomy of `useConfigCatClient()`

Parameters	Description
`providerId`	Optional. Instructs the ConfigCat Client to use a specific `ConfigCatProvider` instead of the default one. Use it if you have multiple `ConfigCatProvider`s in your code. More about multiple providers.

This custom hook returns the ConfigCat instance from the context API. You have to wrap your parent element with ConfigCatProvider to ensure a ConfigCatContextData.

export const FlagDetailsComponent = () => {
  const client = useConfigCatClient();

  const [flagDetails, setFlagDetails] =
    useState<IEvaluationDetails<boolean> | null>(null);

  useEffect(() => {
    client
      .getValueDetailsAsync('isAwesomeFeatureEnabled', false)
      .then((v) => setFlagDetails(v));
  }, [client]);

  return (
    <>{flagDetails && <p>FlagDetails: {JSON.stringify(flagDetails)}</p>}</>
  );
};

Anatomy of `withConfigCatClient()`

Parameters	Description
`providerId`	Optional. Instructs the ConfigCat Client to use a specific `ConfigCatProvider` instead of the default one. Use it if you have multiple `ConfigCatProvider`s in your code. More about multiple providers.

This is a higher-order component that can take your React component and will return the component with the injected ConfigCat related props (WithConfigCatClientProps).

These props are the following:

export interface WithConfigCatClientProps {
  configCatClient: IConfigCatClient;
  getValue: GetValueType;
  lastUpdated?: Date;
}

Sample declaration of class component with ConfigCat SDK's higher-order component:

class MyComponent extends React.Component<
  { myProp: string } & WithConfigCatClientProps
> {
  constructor(props: { myProp: string } & WithConfigCatClientProps) {
    super(props);

    // props.configCatClient - use any method on the instance
    // props.getValue - helper function for flag evaluation
  }

  ...
}

// HOC declaration
const ConfigCatMyComponent = withConfigCatClient(MyComponent);

// Usage of the wrapped component
<ConfigCatMyComponent myProp='ConfigCat <3 React' />

Props - `configCatClient`

The ConfigCat client instance (IConfigCatClient) to access all features of the ConfigCat SDK.

In this example the component can invoke the forceRefreshAsync method on the injected ConfigCat instance.

class ManualRefreshComponent extends React.Component<
  { featureFlagKey: string } & WithConfigCatClientProps,
  { refreshAt: string | null }
> {
  constructor(props: { featureFlagKey: string } & WithConfigCatClientProps) {
    super(props);

    this.state = { refreshAt: '-' };
  }

  refresh() {
    this.props.configCatClient
      .forceRefreshAsync()
      .then(() =>
        this.setState({ refreshAt: new Date().toLocaleTimeString() }),
      );
  }

  render() {
    return (
      <div>
        <button onClick={() => this.refresh()}>Refresh</button>
        <p>Last manual refresh: {this.state.refreshAt}</p>
      </div>
    );
  }
}

const ConfigCatManualRefreshComponent = withConfigCatClient(
  ManualRefreshComponent,
);

Props - `getValue`

A helper function to get the value of a feature flag.

Parameters	Description
`key`	REQUIRED. Setting-specific key. Set on ConfigCat Dashboard for each setting.
`defaultValue`	REQUIRED. This value will be returned in case of an error.
`user`	Optional, User Object. Essential when using Targeting. Read more about Targeting.

class TestHOCComponent extends React.Component<
  WithConfigCatClientProps,
  { isAwesomeFeatureEnabled: string }
> {
  constructor(props: WithConfigCatClientProps) {
    super(props);

    this.state = { isAwesomeFeatureEnabled: false, loading: true };
  }

  componentDidMount() {
    this.evaluateFeatureFlag();
  }

  componentDidUpdate(prevProps: any) {
    // To achieve hot reload on config JSON updates.
    if (prevProps?.lastUpdated !== this.props.lastUpdated) {
      this.evaluateFeatureFlag();
    }
  }

  evaluateFeatureFlag() {
    this.props
      .getValue('isAwesomeFeatureEnabled', false)
      .then((v: boolean) =>
        this.setState({ isAwesomeFeatureEnabled: v, loading: false }),
      );
  }

  render() {
    return loading ? (
      <div>Loading...</div>
    ) : (
      <div>
        Feature flag value: {this.state.isAwesomeFeatureEnabled ? 'ON' : 'OFF'}
      </div>
    );
  }
}

caution

It is important to provide an argument for the defaultValue parameter that matches the type of the feature flag or setting you are evaluating. Please refer to this table for the corresponding types.

Props - `lastUpdated`

The timestamp of when the config was last updated.

User Object

The User Object is essential if you'd like to use ConfigCat's Targeting feature.

For simple targeting:

const userObject = new User('#UNIQUE-USER-IDENTIFIER#');

const userObject = new User('[email protected]');

Parameters	Description
`identifier`	REQUIRED. Unique identifier of a user in your application. Can be any `string` value, even an email address.
`email`	Optional parameter for easier Targeting Rule definitions.
`country`	Optional parameter for easier Targeting Rule definitions.
`custom`	Optional dictionary for custom attributes of a user for advanced Targeting Rule definitions. E.g. User role, Subscription type.

For advanced targeting:

const userObject = new User(
  /* identifier: */ '#UNIQUE-USER-IDENTIFIER#',
  /*      email: */ '[email protected]',
  /*    country: */ 'United Kingdom',
  /*     custom: */ {
    SubscriptionType: 'Pro',
    UserRole: 'Admin',
  },
);

function ButtonComponent() {
  const { value: isAwesomeFeatureEnabled, loading } = useFeatureFlag(
    'isAwesomeFeatureEnabled',
    false,
    userObject,
  );

  return loading ? (
    <div>Loading...</div>
  ) : (
    <div>Feature flag value: {isAwesomeFeatureEnabled ? 'ON' : 'OFF'}</div>
  );
}

The custom dictionary also allows attribute values other than string values:

let userObject = new User('#UNIQUE-USER-IDENTIFIER#');
userObject.custom = {
  Rating: 4.5,
  RegisteredAt: new Date('2023-11-22T12:34:56.000Z'),
  Roles: ['Role1', 'Role2'],
};

User Object Attribute Types

All comparators support string values as User Object attribute (in some cases they need to be provided in a specific format though, see below), but some of them also support other types of values. It depends on the comparator how the values will be handled. The following rules apply:

Text-based comparators (EQUALS, IS ONE OF, etc.)

accept string values,
all other values are automatically converted to string (a warning will be logged but evaluation will continue as normal).

SemVer-based comparators (IS ONE OF, <, >=, etc.)

accept string values containing a properly formatted, valid semver value,
all other values are considered invalid (a warning will be logged and the currently evaluated Targeting Rule will be skipped).

Number-based comparators (=, <, >=, etc.)

accept number values,
accept string values containing a properly formatted, valid number value,
all other values are considered invalid (a warning will be logged and the currently evaluated Targeting Rule will be skipped).

Date time-based comparators (BEFORE / AFTER)

accept Date values, which are automatically converted to a second-based Unix timestamp,
accept number values representing a second-based Unix timestamp,
accept string values containing a properly formatted, valid number value,
all other values are considered invalid (a warning will be logged and the currently evaluated Targeting Rule will be skipped).

String array-based comparators (ARRAY CONTAINS ANY OF / ARRAY NOT CONTAINS ANY OF)

accept arrays of string,
accept string values containing a valid JSON string which can be deserialized to an array of string,
all other values are considered invalid (a warning will be logged and the currently evaluated Targeting Rule will be skipped).

Default user

It's possible to set a default User Object that will be used on feature flag and setting evaluation. It can be useful when your application has a single user only or rarely switches users.

You can set the default User Object either on SDK initialization:

<ConfigCatProvider
  sdkKey="YOUR_SDK_KEY"
  pollingMode={PollingMode.AutoPoll}
  options={{ defaultUser: new User('[email protected]') }}
>
  ...
</ConfigCatProvider>

...or using the setDefaultUser() method of the configCatClient instance:

const CurrentUser: User = new User('[email protected]');

export const SetConfigCatUserComponent = () => {
  const client = useConfigCatClient();

  const [user] = useState(CurrentUser);

  useEffect(() => {
    client.setDefaultUser(user);
  }, [client, user]);

  return null;
};

Whenever the evaluation methods like getValueAsync(), getValueDetailsAsync(), etc. are called without an explicit user parameter, the SDK will automatically use the default user as a User Object.

export const FlagValueDetailsComponent = () => {
  const client = useConfigCatClient();

  const [flagDetails, setFlagDetails] =
    useState<IEvaluationDetails<boolean> | null>(null);

  // invoke getValueDetailsAsync method WITHOUT User Object
  useEffect(() => {
    client
      .getValueDetailsAsync('featureFlagKey', false)
      .then((v) => setFlagDetails(v));
  }, [client]);

  return (
    <>{flagDetails && <p>FlagDetails: {JSON.stringify(flagDetails)}</p>}</>
  );
};

When a user parameter is passed to the evaluation methods, it takes precedence over the default user.

const CurrentUser: User = new User('[email protected]');

export const FlagValueDetailsComponent = () => {
  const client = useConfigCatClient();

  const [flagDetails, setFlagDetails] =
    useState<IEvaluationDetails<boolean> | null>(null);
  const [user] = useState(CurrentUser);

  // invoke getValueDetailsAsync method WITH User Object
  useEffect(() => {
    client
      .getValueDetailsAsync('featureFlagKey', false, user)
      .then((v) => setFlagDetails(v));
  }, [client, user]);

  return (
    <>{flagDetails && <p>FlagDetails: {JSON.stringify(flagDetails)}</p>}</>
  );
};

You can also remove the default user by doing the following:

export const ClearConfigCatUserComponent = () => {
  const client = useConfigCatClient();

  useEffect(() => {
    client.clearDefaultUser();
  }, [client]);

  return null;
};

Polling Modes

The ConfigCat SDK supports 3 different polling mechanisms to acquire the setting values from ConfigCat. After latest setting values are downloaded, they are stored in the local cache, then all getValueAsync() calls are served from there. With the following polling modes, you can customize the SDK to best fit to your application's lifecycle. More about polling modes.

Auto polling (default)

The ConfigCat SDK downloads the latest values and stores them automatically every 60 seconds.

Initialization

<ConfigCatProvider sdkKey="YOUR_SDK_KEY" options={{...}}>
  ...
</ConfigCatProvider>

<ConfigCatProvider sdkKey="YOUR_SDK_KEY" pollingMode={PollingMode.AutoPoll} options={{...}}>
  ...
</ConfigCatProvider>

Use the pollIntervalSeconds option parameter to change the polling interval.

<ConfigCatProvider
  sdkKey="YOUR_SDK_KEY"
  pollingMode={PollingMode.AutoPoll}
  options={{ pollIntervalSeconds: 95 }}
>
  ...
</ConfigCatProvider>

Available options (in addition to the common ones):

Option Parameter	Description	Default
`pollIntervalSeconds`	Polling interval in seconds.	60s
`maxInitWaitTimeSeconds`	Maximum waiting time between the client initialization and the first config acquisition in seconds.	5s

Lazy loading

When calling useFeatureFlag() or WithConfigCatClientProps.getValue(), the ConfigCat SDK downloads the latest setting values if they are not present or expired in the cache.

Initialization

<ConfigCatProvider sdkKey="YOUR_SDK_KEY" pollingMode={PollingMode.LazyLoad} options={{...}}>
  ...
</ConfigCatProvider>

Use cacheTimeToLiveSeconds option parameter to set cache lifetime.

<ConfigCatProvider
  sdkKey="YOUR_SDK_KEY"
  pollingMode="{PollingMode.LazyLoad}"
  options={{ cacheTimeToLiveSeconds: 600 }}
>
  ...
</ConfigCatProvider>

Available options (in addition to the common ones):

Option Parameter	Description	Default
`cacheTimeToLiveSeconds`	Cache TTL in seconds.	60s

Manual polling

Manual polling gives you full control over when the config JSON (with the setting values) is downloaded. ConfigCat SDK will not update them automatically. Calling forceRefreshAsync() is your application's responsibility.

Initialization

<ConfigCatProvider sdkKey="YOUR_SDK_KEY" pollingMode={PollingMode.ManualPoll} options={{...}}>
  ...
</ConfigCatProvider>

const client = useConfigCatClient();
useEffect(() => {
  client.forceRefreshAsync().then(() => {
    console.log('forceRefreshAsync() invoked');
  });
});

SDK Hooks (not React Hooks)

** ConfigCat SDK hooks are different than React Hooks. **

The SDK provides several hooks (events), by means of which you can get notified of its actions. You can subscribe to the following events emitted by the client:

clientReady: This event is emitted when the SDK reaches the ready state. If the SDK is set up to use lazy loading or manual polling, it's considered ready right after syncing up with the config cache. If auto polling is used, the ready state is reached when the SDK has a valid config JSON loaded into memory either from cache or from HTTP. If the config couldn't be loaded neither from cache nor from HTTP, the clientReady event fires when the auto polling's MaxInitWaitTime has passed.
configChanged: This event is emitted first when the SDK loads a valid config JSON into memory from cache, then each time afterwards when a config JSON with changed content is downloaded via HTTP.
flagEvaluated: This event is emitted each time when the SDK evaluates a feature flag or setting. The event provides the same evaluation details that you would get from getValueDetailsAsync().
clientError: This event is emitted when an error occurs within the ConfigCat SDK.

You can subscribe to these events either on initialization:

<ConfigCatProvider
  sdkKey="YOUR_SDK_KEY"
  pollingMode={PollingMode.ManualPoll}
  options={{
    setupHooks: (hooks) =>
      hooks.on('flagEvaluated', () => {
        /* handle the event */
      }),
  }}
>
  ...
</ConfigCatProvider>

...or directly on the ConfigCatClient instance:

export const ConfigCatWithHookComponent = () => {
  const client = useConfigCatClient();

  const [configChangedAt, setConfigChanged] = useState('-');

  useEffect(() => {
    function hookLogic() {
      const t = new Date().toISOString();
      setConfigChanged(t);
      console.log(t);
    }

    client.on('configChanged', hookLogic);

    return () => {
      client.off('configChanged', hookLogic);
    };
  });

  return <p>configChangedAt: {configChangedAt}</p>;
};

Using higher-order component (HOC):

class ConfigChangedComponent extends React.Component<
  WithConfigCatClientProps,
  { refreshAt: string | null }
> {
  constructor(props: WithConfigCatClientProps) {
    super(props);

    this.state = { refreshAt: '-' };
  }

  componentDidMount() {
    this.props.configCatClient.on('configChanged', () => this.myHookLogic());
  }

  componentWillUnmount() {
    this.props.configCatClient.off('configChanged', () => this.myHookLogic());
  }

  myHookLogic() {
    this.setState({ refreshAt: new Date().toISOString() });
  }

  render() {
    return (
      <div>
        <p>configChangedAt: {this.state.refreshAt}</p>
      </div>
    );
  }
}

const ConfigCatManualRefreshComponent = withConfigCatClient(
  ConfigChangedComponent,
);

Online / Offline mode

In cases where you want to prevent the SDK from making HTTP calls, you can switch it to offline mode:

export const ConfigCatIsOfflineComponent = () => {
  const client = useConfigCatClient();

  const [isOffline, setIsOffline] = useState(false);

  function setMode() {
    if (isOffline) {
      client.setOnline();
    } else {
      client.setOffline();
    }

    setIsOffline(client.isOffline);
  }

  return (
    <>
      <p>ConfigCat mode: {isOffline ? 'Offline' : 'Online'}</p>
      <button
        onClick={() => {
          setMode();
        }}
      >
        Set {isOffline ? 'Online' : 'Offline'}
      </button>
    </>
  );
};

In offline mode, the SDK won't initiate HTTP requests and will work only from its cache.

To switch the SDK back to online mode, invoke setOnline() method.

Using the isOffline property you can check whether the SDK is in offline mode or not.

Flag Overrides

With flag overrides you can overwrite the feature flags & settings downloaded from the ConfigCat CDN with local values. Moreover, you can specify how the overrides should apply over the downloaded values. The following 3 behaviours are supported:

Local only (OverrideBehaviour.LocalOnly): When evaluating values, the SDK will not use feature flags & settings from the ConfigCat CDN, but it will use all feature flags & settings that are loaded from local-override sources.
Local over remote (OverrideBehaviour.LocalOverRemote): When evaluating values, the SDK will use all feature flags & settings that are downloaded from the ConfigCat CDN, plus all feature flags & settings that are loaded from local-override sources. If a feature flag or a setting is defined both in the downloaded and the local-override source then the local-override version will take precedence.
Remote over local (OverrideBehaviour.RemoteOverLocal): When evaluating values, the SDK will use all feature flags & settings that are downloaded from the ConfigCat CDN, plus all feature flags & settings that are loaded from local-override sources. If a feature flag or a setting is defined both in the downloaded and the local-override source then the downloaded version will take precedence.

You can load your feature flag & setting overrides from a simple { [key: string]: boolean | string | number } map or query string parameters.

Map

You can set up the SDK to load your feature flag & setting overrides from a { [key: string]: boolean | string | number } map.

const flagOverrides = createFlagOverridesFromMap({
    enabledFeature: true,
    disabledFeature: false,
    intSetting: 5,
    doubleSetting: 3.14,
    stringSetting: "test"
},
OverrideBehaviour.LocalOnly);

<ConfigCatProvider sdkKey="YOUR_SDK_KEY" options={{ flagOverrides }}>
  ...
</ConfigCatProvider>

Query string

Since v4.8.0, it is also possible to override feature flags & settings using query string parameters.

const flagOverrides = createFlagOverridesFromQueryParams(OverrideBehaviour.LocalOverRemote);

<ConfigCatProvider sdkKey="YOUR_SDK_KEY" options={{ flagOverrides }}>
  ...
</ConfigCatProvider>

With that setup, you can override feature flags and settings by appending query string parameters to the URL of your application in the following form: https://app.example.com/?cc-myBooleanFlag=true&cc-myStringSetting=abc&...

The setting type is automatically inferred from the value. Please pay attention to this behavior. The inferred type of the value must match the type of the feature flag or setting you override (see also this table). In case you want to force a boolean or number value to be interpreted as a string value, use the ;str suffix: &cc-myStringSetting;str=true.

If the default prefix used to differentiate between normal and flag override query string parameters (cc-) is not suitable for you, you can set a custom prefix using the corresponding optional parameter of createFlagOverridesFromQueryParams.

Logging

Setting log levels

<ConfigCatProvider
  sdkKey="YOUR_SDK_KEY"
  pollingMode={PollingMode.ManualPoll}
  options={{ logger: createConsoleLogger(LogLevel.Info) }} // Setting log level to Info
>
  ...
</ConfigCatProvider>

Available log levels:

Level	Description
Off	Nothing gets logged.
Error	Only error level events are logged.
Warn	Default. Errors and Warnings are logged.
Info	Errors, Warnings and feature flag evaluation is logged.
Debug	All of the above plus debug info is logged.

Info level logging helps to inspect the feature flag evaluation process:

ConfigCat - INFO - [5000] Evaluating 'isPOCFeatureEnabled' for User '{"Identifier":"#SOME-USER-ID#","Email":"[email protected]"}'
  Evaluating targeting rules and applying the first match if any:
  - IF User.Email CONTAINS ANY OF ['@something.com'] THEN 'false' => no match
  - IF User.Email CONTAINS ANY OF ['@example.com'] THEN 'true' => MATCH, applying rule
  Returning 'true'.

Custom logger implementation

The SDK provides a simple logger implementation that logs to the debugging console (configcat.createConsoleLogger(...)) but it also allows you to inject any custom implementation of IConfigCatLogger.

class MyCustomLogger implements IConfigCatLogger {
  /**
   * Writes an event into the log.
   * @param level Event severity level.
   * @param eventId Event identifier.
   * @param message Message.
   * @param exception The exception object related to the message (if any).
   */
  log(
    level: LogLevel,
    eventId: LogEventId,
    message: LogMessage,
    exception?: any,
  ): void {
    // insert your custom log logic
  }
}

function MyCustomLogger() {}

MyCustomLogger.prototype.log = function (level, eventId, message, exception) {
  // insert your custom log logic
};

then

<ConfigCatProvider
  sdkKey="YOUR_SDK_KEY"
  pollingMode={PollingMode.ManualPoll}
  options={{ cache: new MyCustomLogger() }}
>
  ...
</ConfigCatProvider>

Using custom cache implementation

The ConfigCat SDK stores the downloaded config data in a local cache to minimize network traffic and enhance client performance. If you prefer to use your own cache solution, such as an external or distributed cache in your system, you can implement the IConfigCatCache interface and set the cache property in the options passed to ConfigCatProvider. This allows you to seamlessly integrate ConfigCat with your existing caching infrastructure.

class MyCustomCache implements IConfigCatCache {
  set(key: string, value: string): Promise<void> | void {
    // insert your cache write logic here
  }

  get(
    key: string,
  ): Promise<string | null | undefined> | string | null | undefined {
    // insert your cache read logic here
  }
}

function MyCustomCache() {}

MyCustomCache.prototype.set = function (key, value) {
  // insert your cache write logic here
};
MyCustomCache.prototype.get = function (key) {
  // insert your cache read logic here
};

then

<ConfigCatProvider
  sdkKey="YOUR_SDK_KEY"
  pollingMode={PollingMode.ManualPoll}
  options={{ cache: new MyCustomCache() }}
>
  ...
</ConfigCatProvider>

info

The React SDK supports shared caching. You can read more about this feature and the required minimum SDK versions here.

Sensitive information handling

The frontend/mobile SDKs are running in your users' browsers/devices. The SDK is downloading a config JSON file from ConfigCat's CDN servers. The URL path for this config JSON file contains your SDK key, so the SDK key and the content of your config JSON file (feature flag keys, feature flag values, Targeting Rules, % rules) can be visible to your users. In ConfigCat, all SDK keys are read-only. They only allow downloading your config JSON files, but nobody can make any changes with them in your ConfigCat account.

If you do not want to expose the SDK key or the content of the config JSON file, we recommend using the SDK in your backend components only. You can always create a backend endpoint using the ConfigCat SDK that can evaluate feature flags for a specific user, and call that backend endpoint from your frontend/mobile applications.

Also, we recommend using confidential targeting comparators in the Targeting Rules of those feature flags that are used in the frontend/mobile SDKs.

Using multiple providers

ConfigCatProvider allows you to access the feature flags of a specific Config, identified by the sdkKey parameter. (More precisely, sdkKey identifies a combination of a Config and an Environment.)

However, in some cases, you may want to access feature flags from multiple Configs in your application. To do this, you will need to use multiple ConfigCatProviders — each associated with a specific Config by providing the corresponding sdkKey.

It's also important to keep in mind that useFeatureFlag calls will default to using the nearest ConfigCatProvider, similar to how React's useContext works.

So, when working with multiple providers, it may be necessary to differentiate between them. You can achieve this by assigning a unique id to each provider. (Note that the absence of id also acts as a unique identifier.)

Then, by passing the provider id in your useFeatureFlag, useConfigCatClient, or similar calls, you can explicitly specify which provider (i.e. which sdkKey, and ultimately which Config and Environment) to use.

const CC_PROVIDER_ID_COMMON = "COMMON";
const CC_PROVIDER_ID_FRONTEND = "FRONTEND";

<ConfigCatProvider sdkKey="#YOUR_COMMON_SDK_KEY#" id={CC_PROVIDER_ID_COMMON}> 
  <ConfigCatProvider sdkKey="#YOUR_FRONTEND_SDK_KEY#" id={CC_PROVIDER_ID_FRONTEND}>
      ...
      const myFeatureInCommon = useFeatureFlag("myFeatureInCommon", false, void 0, CC_PROVIDER_ID_COMMON)

      const myFeatureInFrontEnd = useFeatureFlag("myFeatureInFrontEnd", false, void 0, CC_PROVIDER_ID_FRONTEND)
      ...
  </ConfigCatProvider>
</ConfigCatProvider>

When you are using multiple providers and they are not nested, it is not necessary to specify the id attribute:

<ConfigCatProvider sdkKey="#YOUR_COMMON_SDK_KEY#">
  ...
  const myFeatureInCommon = useFeatureFlag("myFeatureInCommon", false);
  ...
</ConfigCatProvider>

<ConfigCatProvider sdkKey="#YOUR_FRONTEND_SDK_KEY#">
  ...
  const myFeatureInFrontEnd = useFeatureFlag("myFeatureInFrontEnd", false);
  ...
</ConfigCatProvider>

If you are using higher order components, you can set the providerId parameter in the withConfigCatClient function.

React SDK Reference

Getting started

1. Install package

2. Import and initialize a `ConfigCatProvider` with your SDK Key

3. Get your setting value

Creating the ConfigCat Client

Acquire the ConfigCat instance

Anatomy of `useFeatureFlag()`

Setting type mapping

Anatomy of `useConfigCatClient()`

Anatomy of `withConfigCatClient()`

Props - `configCatClient`

Props - `getValue`

Props - `lastUpdated`

User Object

User Object Attribute Types

Default user

Polling Modes

Auto polling (default)

Initialization

Lazy loading

Initialization

Manual polling

Initialization

SDK Hooks (not React Hooks)

Online / Offline mode

Flag Overrides

Map

Query string

Logging

Setting log levels

Custom logger implementation

Using custom cache implementation

Sensitive information handling

Using multiple providers

Sample Application

Guides

Look under the hood

Getting started​

1. Install package​

2. Import and initialize a ConfigCatProvider with your SDK Key​

3. Get your setting value​

Creating the ConfigCat Client​

Acquire the ConfigCat instance​

Anatomy of useFeatureFlag()​

Setting type mapping​

Anatomy of useConfigCatClient()​

Anatomy of withConfigCatClient()​

Props - configCatClient​

Props - getValue​

Props - lastUpdated​

User Object​

User Object Attribute Types​

Default user​

Polling Modes​

Auto polling (default)​

Initialization​

Lazy loading​

Initialization​

Manual polling​

Initialization​

SDK Hooks (not React Hooks)​

Online / Offline mode​

Flag Overrides​

Map​

Query string​

Logging​

Setting log levels​

Custom logger implementation​

Using custom cache implementation​

Sensitive information handling​

Using multiple providers​

Sample Application​

Guides​

Look under the hood​

Getting started

1. Install package

2. Import and initialize a `ConfigCatProvider` with your SDK Key

3. Get your setting value

Creating the ConfigCat Client

Acquire the ConfigCat instance

Anatomy of `useFeatureFlag()`

Setting type mapping

Anatomy of `useConfigCatClient()`

Anatomy of `withConfigCatClient()`

Props - `configCatClient`

Props - `getValue`

Props - `lastUpdated`

User Object

User Object Attribute Types

Default user

Polling Modes

Auto polling (default)

Initialization

Lazy loading

Initialization

Manual polling

Initialization

SDK Hooks (not React Hooks)

Online / Offline mode

Flag Overrides

Map

Query string

Logging

Setting log levels

Custom logger implementation

Using custom cache implementation

Sensitive information handling

Using multiple providers

Sample Application

Guides

Look under the hood