GrowthBook is a GrowthBook SDK for Elixir/OTP.

This SDK follows the guidelines set out in GrowthBook's documentation, and the API is tested on conformance with the test cases from the JS SDK.

To ensure an Elixir-friendly API, the implementation deviates from the official SDK in the following ways:

• Instead of tuple-lists, this library uses actual tuples
• Comparisons with undefined are implemented by using :undefined
• Function names are converted to snake_case, and is_ prefix is replaced with a ? suffix
• Instead of classes, a Context struct is used (similar to %Plug.Conn{} in plug)

What is GrowthBook?

GrowthBook is an open source A/B testing platform. The platform works significantly different from other A/B testing platforms, most notably: it is language agnostic.

Clients by default work offline, and manage their own data. This means that you are free to implement A/B tests server-side, or client-side without worrying about things like "anti-flicker" scripts, or the added latency of JS embeds.

Furthermore, GrowthBook supports both experiments (A/B tests and multivariate tests) and feature flags. Because all logic to run experiments and feature flags is contained in the library, there is virtually no added latency to running experiments or using feature flags.

Installation

Add growthbook to your list of dependencies in mix.exs:

def deps do
  [
    {:growthbook, "~> 0.2"}
  ]
end

Usage

# Create a context, which can be reused for multiple users
# Approach 1: Manual Feature Configuration
features_config = Jason.decode!("""
{
  "features": {
    "send-reminder": {
      "defaultValue": false,
      "rules": [{ "condition": { "browser": "chrome" }, "force": true }]
    },
    "add-to-cart-btn-color": {
      "rules": [{ "variations": [{ "color": "red" }, { "color": "green" }] }]
    }
  }
}
""")

features = GrowthBook.Config.features_from_config(features_config)

context = GrowthBook.build_context(
  %{
    "id" => "12345",
    "country_code" => "NL",
    "browser" => "chrome"
  },
  features  # Explicitly provide features
)

# Approach 2: Auto-refreshing Features
case GrowthBook.init(
  client_key: "key_prod_123...",
  api_host: "https://cdn.growthbook.io",
  decryption_key: "key_123...",
  swr_ttl_seconds: 60,
  on_refresh: fn features ->
    Logger.info("Features refreshed: #{map_size(features)} available")
    MyApp.FeatureNotifier.features_updated(features)
  end
) do
  {:ok, :initialized} -> # Features loaded successfully
    # Start using GrowthBook...
  {:error, reason} -> # Handle error
    # Handle initialization failure...
end

# Create context that automatically uses latest features
context = GrowthBook.build_context(%{
  "id" => "12345",
  "country_code" => "NL",
  "browser" => "chrome"
})

# Usage is the same for both approaches:

# Use a feature toggle
if GrowthBook.feature(context, "send-reminder").on? do
  Logger.info("Sending reminder")
end

# Use a feature's value
color = GrowthBook.feature(context, "add-to-cart-btn-color").value["color"]
Logger.info("Color: " <> color)

# Run an inline experiment
if GrowthBook.run(context, %GrowthBook.Experiment{
  key: "checkout-v2",
  active?: true,
  coverage: 1,
  variations: [1, 2]
}).in_experiment? do
  Logger.info("In experiment")
end

Auto-Refresh Features

GrowthBook now supports automatic feature refreshing from your GrowthBook API. Instead of manually managing features, you can initialize GrowthBook with your API credentials.

Core Components

1. GenServer-Based Repository: Implemented as a GenServer that maintains feature state in memory (with stale-while-revalidate (SWR) caching strategy) that handles fetching, caching of features and refresh cycles based on configuration.

# Initialize GrowthBook with auto-refresh
case GrowthBook.init(
  client_key: "key_prod_123...",
  api_host: "https://cdn.growthbook.io",
  decryption_key: "key_123...",  # Optional: Required for encrypted features
  swr_ttl_seconds: 60,  # Optional: Default is 60 seconds
  refresh_strategy: :periodic,  # Optional: :periodic (default) or :manual
  on_refresh: fn features ->  # Optional: Callback when features are refreshed
    Logger.info("Features refreshed: #{map_size(features)} available")
    # Notify your application about new features
    MyApp.FeatureNotifier.features_updated(features)
  end
) do
  {:ok, :initialized} -> # Features loaded successfully
    # Start using GrowthBook...
  {:error, reason} -> # Handle error
    # Handle initialization failure...
end

# Create context that automatically uses latest features
context = GrowthBook.build_context(%{
  "id" => "12345",
  "country_code" => "NL",
  "browser" => "chrome"
})

# Features will automatically refresh in the background
# All feature evaluations will use the latest features
if GrowthBook.feature(context, "send-reminder").on? do
  Logger.info("Sending reminder")
end

Refresh Strategies

The SDK supports two refresh strategies:

• :periodic (default): Features are automatically refreshed in the background based on the TTL.
• :manual: Features are only refreshed when explicitly called with GrowthBook.FeatureRepository.refresh().

Shutting Down

When your application is shutting down or you no longer need the feature repository, stop it properly to release resources:

# Stops the FeatureRepository GenServer
GenServer.stop(GrowthBook.FeatureRepository)

Supervision

Since the FeatureRepository is a GenServer, it's recommended to add it to your application's supervision tree for proper lifecycle management:

# In your application.ex
def start(_type, _args) do
  children = [
    # Other children...
    
    # Add GrowthBook FeatureRepository to supervision tree
    {GrowthBook.FeatureRepository, 
      client_key: "key_prod_123...",
      api_host: "https://cdn.growthbook.io",
      # Add other options as needed
    }
  ]

  opts = [strategy: :one_for_one, name: MyApp.Supervisor]
  Supervisor.start_link(children, opts)
  
  # Then initialize GrowthBook
  case GrowthBook.FeatureRepository.await_initialization(GrowthBook.FeatureRepository, 5000) do
    :ok -> 
      Logger.info("GrowthBook features initialized successfully")
    {:error, reason} -> 
      Logger.error("Failed to initialize GrowthBook features: #{reason}")
  end
  
  {:ok, self()}
end

Key improvements:

• Auto-refresh: Features automatically refresh from your GrowthBook API
• Encryption: Support for encrypted feature payloads
• Callbacks: Get notified when features are updated
• Resilient: Keeps existing features on API errors
• Configurable: Control refresh intervals and strategies

License

This library is MIT licensed. See the LICENSE file in this repository for details.