An SDK evaluates features and variables inside your application, from a datafile it holds in memory and the context you pass. No decision needs a network request.

How evaluation works#

Your application fetches a datafile, creates an SDK instance with it, and asks for values with a context. In JavaScript:

import { createFeaturevisor } from '@featurevisor/sdk'
const f = createFeaturevisor({
  datafile: datafileContent,
})
const context = {
  userId: 'user-4',
  country: 'nl',
}
f.isEnabled('checkout', context)
f.getVariation('pricing', context)
f.getVariable('buyButton', 'label', context)
f.getVariable('supportEmail', context)

isEnabled reads a flag and getVariation a variation. getVariable reads a feature variable when given a feature and a variable key, and a global variable when given one key. For user-4, a Dutch user, they return:

Other languages have the same calls with their own naming, and some read global variables with a separate method.

Create one instance and reuse it. When a newer datafile arrives, give it to the same instance, as Deployment describes. Check your SDK's datafile API for whether an update merges or replaces, since a merge keeps definitions the new file left out.

The SDK makes no network requests. The context you pass, such as a user's country or plan, stays in your application unless your own code sends it somewhere.

A datafile in a browser or a mobile app can be read by its users. Keep secrets out of it.

Choose an SDK#

• The JavaScript SDK has guides for Node.js and the browser.
• Kotlin uses the Java SDK.
• Major versions differ by language. Supported SDK versions lists the first version of each with v4 support.
• Java packages come from GitHub Packages, which requires authentication even for public packages.

Frameworks#

Framework guides build on the JavaScript SDK, with helpers that fit each framework:

• React and React Native
• Next.js
• Vue.js and Nuxt
• Astro
• Express.js and Fastify

OpenFeature#

If your application already uses OpenFeature, a Featurevisor provider plugs into it. Providers exist for Node.js, browsers, Go, Swift, Java and Kotlin, Ruby, Python, PHP, Rust and Elixir. They are optional. See OpenFeature.

Related#

• Quick start
• Deployment
• Supported SDK versions