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Using Feature Flags In Code

Overview​

This guide provides a high-level overview on using Feature Flags in your application. For a more detailed guide on a particular SDK, refer to the SDK documentation.

Providing User Data​

When getting Feature Flags from the AppFlags client, you need to provide some data about your user. At minimum, you need to provide a unique key for each of your users. This is a string that must be unique for each user and not change.

For example, in Javascript, a basic user looks like this:

const user = {
    key: "<unique_user_key>"
};

In a client-side SDK, you need to provide user information when initializing the AppFlags client.

In a server-side SDK, you need to provide user information when getting Feature Flags.

Getting Feature Flags​

You can get a Feature Flag from the AppFlags client by specifying the flag's key.

For example, in Javascript, getting a Feature Flag looks like this:

const flag = appflagsClient.getFlag("flag_key");

In a server-side SDK, you will also need to specify the user. For example, in Node.js, getting a Feature Flag looks like this: 

const flag = appflagsClient.getFlag(user, "flag_key");

For more details on getting Feature Flags and additional SDK functionality, refer to the SDK documentation for the specific SDK that you are using.

Getting Realtime Feature Flag Updates​

When you modify a Feature Flag in the AppFlags dashboard, the AppFlags client in your application immediately receives the updated Feature Flag. This allows your app to immediately react to Feature Flag changes.

Client-side SDK Realtime Updates​

In a client-side SDK, you can set up a callback to get notified when a particular Feature Flag is modified for the user.

For example, in Javascript, you can subscribe to Feature Flag updates with a callback like this:

appFlagsClient.onFlagChanged("flag_key", flag => {
    // handle the updated feature flag
});

Server-side SDK Realtime Updates​

In a server-side SDK, you can set up a callback to get notified when any Feature Flags have been updated.

For example, in Node, you can subscribe to Feature Flag updates with a callback like this:

appflagsClient.onFlagsChanged(() => {
    // handle flags changing
});

Additional SDK Functionality​

The above examples highlight a few basic uses of the AppFlags SDK. For a full reference, refer to the SDK documentation.