Client-side SDKs

Overview

Harness FME provides client-side SDKs that let you evaluate feature flags, run experiments, and deliver personalized experiences directly in your application's frontend.

These SDKs are optimized for real-time updates and minimal latency, ensuring that your users always experience the most up-to-date feature set.

Does the SDK cache expire?

The Split mobile (iOS and Android) and JavaScript Browser SDKs download a local cache of flag data and store it in the device or browser file system. This cache has a default expiration period of 10 days in most SDKs, after which the SDK refreshes the cache from scratch.

The default and configuration options differ slightly by SDK:

• JavaScript SDK (v11.2.0 and later): Default expiration of 10 days, configurable via the LOCALSTORAGE setting.
• Browser SDK (v1.2.0 and later): Default expiration of 10 days, configurable via the InLocalStorage setting. See Configuring LocalStorage cache for the SDK.
• Android SDK (v5.3.0 and later): Default expiration of 10 days, configurable via the rolloutCacheConfiguration setting.
• iOS SDK (v3.3.0 and later): Default expiration of 10 days, configurable via the rolloutCacheConfiguration setting.

All SDKs continue to store impressions and events for up to 90 days. After that period, the cache is considered stale and may be purged.

How to initialize for multiple user IDs?

The JavaScript SDK supports initializing multiple client objects from the same SDK factory, each with a unique user key (user ID), like so:

client1 = factory.client("user_id1");
client2 = factory.client("user_id2");

However, iOS and Android SDKs don’t support this feature. How can multiple users be handled in mobile SDKs?

Since iOS and Android SDKs don’t allow multiple clients from the same factory instance, the recommended approach is to initialize a separate factory object for each user ID.

Each factory creates a local cache folder named using the SDK API key. To avoid cache conflicts, you should use a different SDK API key per factory so each instance maintains its own cache and updates independently.

Feature flag update timing

When you make changes to a feature flag in the Harness UI, mobile (iOS, Android) and JavaScript Browser SDKs may not reflect the update immediately for all users.

Updates roll out gradually (some devices sync within the first day, with more devices updating in the following days) unless your code waits for the SDK_READY event. If your app only uses cached data from the previous session (triggered by SDK_READY_FROM_CACHE), users may continue to see the old values until their cache syncs.

To ensure the latest changes are reflected, calculate treatments after the SDK_READY event fires, and update them if the value changes after initial load.

Get started

Select a platform to start integrating FME into your client application.

SDK	API Key/Type	Links
Android	client-side	Docs, GitHub
Angular utilities	client-side	Docs, GitHub
Browser	client-side	Docs, GitHub
Flutter plugin	client-side	Docs, GitHub
iOS	client-side	Docs, GitHub
JavaScript	client-side	Docs, GitHub
React Native	client-side	Docs, GitHub
React	client-side	Docs, GitHub
Redux	client-side	Docs, GitHub