dependent-flags-demo

A demonstration of a simple stateless implementation of "flag dependencies" with Optimizely Full Stack

Try it out

Check out the demo here.

The source code is in the docs directory in this repository.

What are stateless flag dependencies?

Imagine you're working with three Optimizely Full Stack Feature Flags:,flag_1, flag_2, and flag_3:

• flag_1 and flag_2 each have their own flag rules.
• flag_3 should be on for everyone for whom flag_1 and flag_2 are also on.

In this scenario, flag_3 depends on flag_1 and flag_2. When a decision for flag_3 is made, these dependencies can be evaluated statelessly or statefully:

• Stateless dependency evaluation works by checking whether flag_1 and flag_2 are on for a given user at the moment that a decision for flag_3 is required.
• Stateful dependency evaluation works by checking whether flag_1 and flag_2 were explicitly evaluated as on for a given user at some point before a decision is required for flag_3.

This demo implements stateless flag dependencies.

How to specify a dependency

With this approach, a Full Stack user can specify flag dependencies in the Optimizely Full Stack UI by adding a special _depends flag variable:

Dependencies are specified in the default value of the _depends variable using a comma-separated list of flag keys.

How it works (implementation)

optimizely_flag_dependencies.js exports one function: createInstance().

This function behaves exactly like the Optimizely Full Stack createInstance() method with one difference:

optimizely_flag_dependencies.createInstance() returns an Optimizely client instance with an additional bound method, decideWithDependencies().

The following code example captures the relationship between optimizelyClient.decideDependencies() and user.decide():

import * as optimizely_flag_dependencies from "./optimizely_flag_dependencies.js";

// Instantiate an Optimizely client object
var optimizelyClient = optimizely_flag_dependencies.createInstance({ sdkKey: "LbmzK7viE2J2bP5ozmZR9" });

// Create a user context object
var user = optimizelyClient.createUserContext("user123");

// Decide whether `flag_3` is enabled for `user123`, ignoring any dependencies
var decisionWithoutDependencies = user.decide("flag_3");

// Decide whether `flag_3` is enabled for `user123` only if all dependencies are also enabled right now
var decisionWithDependencies = optimizelyClient.decideWithDependencies(user, "flag_3")