Eppo React Native SDK

Eppo is a modular flagging and experimentation analysis tool. Eppo's React Native SDK is built to make assignments for single user client applications that run in a web browser. Before proceeding you'll need an Eppo account.

Features

• Feature gates
• Kill switches
• Progressive rollouts
• A/B/n experiments
• Mutually exclusive experiments (Layers)
• Dynamic configuration

Installation

npm install @eppo/react-native-sdk

Quick start

Begin by initializing a singleton instance of Eppo's client. Once initialized, the client can be used to make assignments anywhere in your app.

Initialize once

import { init } from "@eppo/react-native-sdk";

await init({ apiKey: "<SDK-KEY-FROM-DASHBOARD>" });

Assign anywhere

import * as EppoSdk from "@eppo/react-native-sdk";

const eppoClient = EppoSdk.getInstance();
const user = getCurrentUser();

const variation = eppoClient.getBooleanAssignment('show-new-feature', user.id, { 
  'country': user.country,
  'device': user.device,
}, false);

Assignment functions

Every Eppo flag has a return type that is set once on creation in the dashboard. Once a flag is created, assignments in code should be made using the corresponding typed function:

getBoolAssignment(...)
getNumericAssignment(...)
getIntegerAssignment(...)
getStringAssignment(...)
getJSONAssignment(...)

Each function has the same signature, but returns the type in the function name. For booleans use getBooleanAssignment, which has the following signature:

getBooleanAssignment: (
  flagKey: string,
  subjectKey: string,
  subjectAttributes: Record<string, any>,
  defaultValue: boolean,
) => boolean

Initialization options

The init function accepts the following optional configuration arguments.

Assignment logger

To use the Eppo SDK for experiments that require analysis, pass in a callback logging function to the init function on SDK initialization. The SDK invokes the callback to capture assignment data whenever a variation is assigned. The assignment data is needed in the warehouse to perform analysis.

The code below illustrates an example implementation of a logging callback using Segment, but you can use any system you'd like. The only requirement is that the SDK receives a logAssignment callback function. Here we define an implementation of the Eppo IAssignmentLogger interface containing a single function named logAssignment:

import { IAssignmentLogger } from "@eppo/react-native-sdk";
import { AnalyticsBrowser } from "@segment/analytics-next";

// Connect to Segment (or your own event-tracking system)
const analytics = AnalyticsBrowser.load({ writeKey: "<SEGMENT_WRITE_KEY>" });

const assignmentLogger: IAssignmentLogger = {
  logAssignment(assignment) {
    analytics.track({
      userId: assignment.subject,
      event: "Eppo Randomized Assignment",
      type: "track",
      properties: { ...assignment },
    });
  },
};

Avoiding duplicated assignment logs

Eppo's SDK uses an internal cache to ensure that duplicate assignment events are not logged to the data warehouse. While Eppo's analytic engine will automatically deduplicate assignment records, this internal cache prevents firing unnecessary events and can help minimize costs associated with event logging.

Philosophy

Eppo's SDKs are built for simplicity, speed and reliability. Flag configurations are compressed and distributed over a global CDN (Fastly), typically reaching end users in under 15ms. Those configurations are then cached locally, ensuring that each assignment is made instantly. Each SDK is as light as possible, with evaluation logic at around 25 simple lines of code. The simple typed functions listed above are all developers need to know about, abstracting away the complexity of the underlying set of features.