@openfeature/web-sdk

<p align="center"> <picture> <source media="(prefers-color-scheme: dark)" srcset="https://raw.githubusercontent.com/open-feature/community/0e23508c163a6a1ac8c0ced3e4bd78faafe627c7/assets/logo/horizontal/white/openfeature-horizontal-white.svg" /> <img align="center" alt="OpenFeature Logo" src="https://raw.githubusercontent.com/open-feature/community/0e23508c163a6a1ac8c0ced3e4bd78faafe627c7/assets/logo/horizontal/black/openfeature-horizontal-black.svg" /> </picture> </p> <h2 align="center">OpenFeature Web SDK</h2>   <p align="center" class="github-badges"> <a href="https://github.com/open-feature/spec/releases/tag/v0.8.0"> <img alt="Specification" src="https://img.shields.io/static/v1?label=specification&message=v0.8.0&color=yellow&style=for-the-badge" /> </a>  <a href="https://github.com/open-feature/js-sdk/releases/tag/web-sdk-v1.4.1"> <img alt="Release" src="https://img.shields.io/static/v1?label=release&message=v1.4.1&color=blue&style=for-the-badge" /> </a>  <br/> <a href="https://open-feature.github.io/js-sdk/modules/_openfeature_web_sdk.html"> <img alt="API Reference" src="https://img.shields.io/badge/reference-teal?logo=javascript&logoColor=white" /> </a> <a href="https://www.npmjs.com/package/@openfeature/web-sdk"> <img alt="NPM Download" src="https://img.shields.io/npm/dm/%40openfeature%2Fweb-sdk" /> </a> <a href="https://codecov.io/gh/open-feature/js-sdk"> <img alt="codecov" src="https://codecov.io/gh/open-feature/js-sdk/branch/main/graph/badge.svg?token=3DC5XOEHMY" /> </a> <a href="https://bestpractices.coreinfrastructure.org/projects/6594"> <img alt="CII Best Practices" src="https://bestpractices.coreinfrastructure.org/projects/6594/badge" /> </a> </p>  [OpenFeature](https://openfeature.dev) is an open specification that provides a vendor-agnostic, community-driven API for feature flagging that works with your favorite feature flag management tool or in-house solution.  ## 🚀 Quick start ### Requirements - ES2015-compatible web browser (Chrome, Edge, Firefox, etc) ### Install #### npm ```sh npm install --save @openfeature/web-sdk ``` > [!TIP] > This SDK is designed to run in the browser. If you're interested in server support, check out the [Node.js SDK](https://openfeature.dev/docs/reference/technologies/server/javascript/). #### yarn ```sh # yarn requires manual installation of the @openfeature/core peer-dependency yarn add @openfeature/web-sdk @openfeature/core ``` > [!NOTE] > `@openfeature/core` contains common components used by all OpenFeature JavaScript implementations. > Every SDK version has a requirement on a single, specific version of this dependency. > For more information, and similar implications on libraries developed with OpenFeature see [considerations when extending](#considerations). ### Usage ```ts import { OpenFeature } from '@openfeature/web-sdk'; // Register your feature flag provider await OpenFeature.setProviderAndWait(new YourProviderOfChoice()); // create a new client const client = OpenFeature.getClient(); // Evaluate your feature flag const v2Enabled = client.getBooleanValue('v2_enabled', false); if (v2Enabled) { console.log("v2 is enabled"); } ``` ### API Reference See [here](https://open-feature.github.io/js-sdk/modules/_openfeature_web_sdk.html) for the complete API documentation. ## 🌟 Features | Status | Features | Description | | ------ | ----------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------- | | ✅ | [Providers](#providers) | Integrate with a commercial, open source, or in-house feature management tool. | | ✅ | [Targeting](#targeting-and-context) | Contextually-aware flag evaluation using [evaluation context](https://openfeature.dev/docs/reference/concepts/evaluation-context). | | ✅ | [Hooks](#hooks) | Add functionality to various stages of the flag evaluation life-cycle. | | ✅ | [Logging](#logging) | Integrate with popular logging packages. | | ✅ | [Domains](#domains) | Logically bind clients with providers. | | ✅ | [Eventing](#eventing) | React to state changes in the provider or flag management system. | | ✅ | [Tracking](#tracking) | Associate user actions with feature flag evaluations, particularly for A/B testing. | | ✅ | [Shutdown](#shutdown) | Gracefully clean up a provider during application shutdown. | | ✅ | [Extending](#extending) | Extend OpenFeature with custom providers and hooks. | <sub>Implemented: ✅ | In-progress: ⚠️ | Not implemented yet: ❌</sub> ### Providers [Providers](https://openfeature.dev/docs/reference/concepts/provider) are an abstraction between a flag management system and the OpenFeature SDK. Look [here](https://openfeature.dev/ecosystem/?instant_search%5BrefinementList%5D%5Btype%5D%5B0%5D=Provider&instant_search%5BrefinementList%5D%5Bcategory%5D%5B0%5D=Client-side&instant_search%5BrefinementList%5D%5Btechnology%5D%5B0%5D=JavaScript) for a complete list of available providers. If the provider you're looking for hasn't been created yet, see the [develop a provider](#develop-a-provider) section to learn how to build it yourself. Once you've added a provider as a dependency, it can be registered with OpenFeature like this: #### Awaitable To register a provider and ensure it is ready before further actions are taken, you can use the `setProviderAndWait` method as shown below: ```ts await OpenFeature.setProviderAndWait(new MyProvider()); ``` #### Synchronous To register a provider in a synchronous manner, you can use the `setProvider` method as shown below: ```ts OpenFeature.setProvider(new MyProvider()); ``` Once the provider has been registered, the status can be tracked using [events](#eventing). In some situations, it may be beneficial to register multiple providers in the same application. This is possible using [domains](#domains), which is covered in more detail below. ### Flag evaluation flow When a new provider is added to OpenFeature client the following process happens: ```mermaid sequenceDiagram autonumber Client-->+Feature Flag Provider: ResolveAll (context) Feature Flag Provider-->-Client: Flags values ``` In (1) the Client sends a request to the provider backend in order to get all values from all feature flags that it has. Once the provider backend replies (2) the client holds all flag values and therefore the flag evaluation process is synchronous. In order to prevent flag evaluations from defaulting while the provider is initializing, it is highly recommended to evaluate flags only after the provider is ready. This can be done using the `setProviderAndWait` method or using the `setProvider` method and listening for the `READY` [event](#eventing). ### Targeting and Context Sometimes, the value of a flag must consider some dynamic criteria about the application or user, such as the user's location, IP, email address, or the server's location. In OpenFeature, we refer to this as [targeting](https://openfeature.dev/specification/glossary#targeting). If the flag management system you're using supports targeting, you can provide the input data using the [evaluation context](https://openfeature.dev/docs/reference/concepts/evaluation-context). ```ts // Sets global context during provider registration await OpenFeature.setProvider(new MyProvider(), { origin: document.location.host }); ``` Change context after the provider has been registered using `setContext`. ```ts // Set a value to the global context await OpenFeature.setContext({ targetingKey: localStorage.getItem("targetingKey") }); ``` Context is global and setting it is `async`. Providers may implement an `onContextChanged` method that receives the old and newer contexts. Given a context change, providers can use this method internally to detect if the flag values cached on the client are still valid. If needed, a request will be made to the provider with the new context in order to get the correct flag values. ### Hooks [Hooks](https://openfeature.dev/docs/reference/concepts/hooks) allow for custom logic to be added at well-defined points of the flag evaluation life-cycle. Look [here](https://openfeature.dev/ecosystem/?instant_search%5BrefinementList%5D%5Btype%5D%5B0%5D=Hook&instant_search%5BrefinementList%5D%5Bcategory%5D%5B0%5D=Client-side&instant_search%5BrefinementList%5D%5Btechnology%5D%5B0%5D=JavaScript) for a complete list of available hooks. If the hook you're looking for hasn't been created yet, see the [develop a hook](#develop-a-hook) section to learn how to build it yourself. Once you've added a hook as a dependency, it can be registered at the global, client, or flag invocation level. ```ts import { OpenFeature } from "@openfeature/web-sdk"; // add a hook globally, to run on all evaluations OpenFeature.addHooks(new ExampleGlobalHook()); // add a hook on this client, to run on all evaluations made by this client const client = OpenFeature.getClient(); client.addHooks(new ExampleClientHook()); // add a hook for this evaluation only const boolValue = client.getBooleanValue("bool-flag", false, { hooks: [new ExampleHook()]}); ``` ### Logging The Web SDK will log warnings and errors to the console by default. This behavior can be overridden by passing a custom logger either globally or per client. A custom logger must implement the [Logger interface](../shared/src/logger/logger.ts). ```ts import type { Logger } from "@openfeature/web-sdk"; // The logger can be anything that conforms with the Logger interface const logger: Logger = console; // Sets a global logger OpenFeature.setLogger(logger); // Sets a client logger const client = OpenFeature.getClient(); client.setLogger(logger); ``` ### Domains Clients can be assigned to a domain. A domain is a logical identifier which can be used to associate clients with a particular provider. If a domain has no associated provider, the default provider is used. ```ts import { OpenFeature, InMemoryProvider } from "@openfeature/web-sdk"; // Registering the default provider OpenFeature.setProvider(InMemoryProvider(myFlags)); // Registering a provider to a domain OpenFeature.setProvider("my-domain", new InMemoryProvider(someOtherFlags)); // A Client bound to the default provider const clientWithDefault = OpenFeature.getClient(); // A Client bound to the InMemoryProvider provider const domainScopedClient = OpenFeature.getClient("my-domain"); ``` Domains can be defined on a provider during registration. For more details, please refer to the [providers](#providers) section. #### Manage evaluation context for domains By default, domain-scoped clients use the global context. This can be overridden by explicitly setting context when registering the provider or by referencing the domain when updating context: ```ts OpenFeature.setProvider("my-domain", new NewCachedProvider(), { targetingKey: localStorage.getItem("targetingKey") }); ``` To change context after the provider has been registered, use `setContext` with a domain: ```ts await OpenFeature.setContext("my-domain", { targetingKey: localStorage.getItem("targetingKey") }) ``` Once a domain's context has been defined, it will override the global context for all clients bound to the domain. Context can be cleared for a domain by calling `OpenFeature.clearContext("my-domain")` or `OpenFeature.clearContexts()` to reset all context. ### Eventing Events allow you to react to state changes in the provider or underlying flag management system, such as flag definition changes, provider readiness, or error conditions. Initialization events (`PROVIDER_READY` on success, `PROVIDER_ERROR` on failure) are dispatched for every provider. Some providers support additional events, such as `PROVIDER_CONFIGURATION_CHANGED`. Please refer to the documentation of the provider you're using to see what events are supported. ```ts import { OpenFeature, ProviderEvents } from '@openfeature/web-sdk'; // OpenFeature API OpenFeature.addHandler(ProviderEvents.Ready, (eventDetails) => { console.log(`Ready event from: ${eventDetails?.providerName}:`, eventDetails); }); // Specific client const client = OpenFeature.getClient(); client.addHandler(ProviderEvents.Error, (eventDetails) => { console.log(`Error event from: ${eventDetails?.providerName}:`, eventDetails); }); ``` ### Tracking The tracking API allows you to use OpenFeature abstractions and objects to associate user actions with feature flag evaluations. This is essential for robust experimentation powered by feature flags. For example, a flag enhancing the appearance of a UI component might drive user engagement to a new feature; to test this hypothesis, telemetry collected by a [hook](#hooks) or [provider](#providers) can be associated with telemetry reported in the client's `track` function. ```ts // flag is evaluated client.getBooleanValue('new-feature', false); // new feature is used and track function is called recording the usage useNewFeature(); client.track('new-feature-used'); ``` ### Shutdown The OpenFeature API provides a close function to perform a cleanup of all registered providers. This should only be called when your application is in the process of shutting down. ```ts import { OpenFeature } from '@openfeature/web-sdk'; await OpenFeature.close() ``` ## Extending ### Develop a provider To develop a provider, you need to create a new project and include the OpenFeature SDK as a dependency. This can be a new repository or included in [the existing contrib repository](https://github.com/open-feature/js-sdk-contrib) available under the OpenFeature organization. You’ll then need to write the provider by implementing the [Provider interface](./src/provider/provider.ts) exported by the OpenFeature SDK. ```ts import { AnyProviderEvent, EvaluationContext, Hook, JsonValue, Logger, Provider, ProviderEventEmitter, ResolutionDetails } from '@openfeature/web-sdk'; // implement the provider interface class MyProvider implements Provider { // Adds runtime validation that the provider is used with the expected SDK public readonly runsOn = 'client'; readonly metadata = { name: 'My Provider', } as const; // Optional provider managed hooks hooks?: Hook[]; resolveBooleanEvaluation(flagKey: string, defaultValue: boolean, context: EvaluationContext, logger: Logger): ResolutionDetails<boolean> { // code to evaluate a boolean } resolveStringEvaluation(flagKey: string, defaultValue: string, context: EvaluationContext, logger: Logger): ResolutionDetails<string> { // code to evaluate a string } resolveNumberEvaluation(flagKey: string, defaultValue: number, context: EvaluationContext, logger: Logger): ResolutionDetails<number> { // code to evaluate a number } resolveObjectEvaluation<T extends JsonValue>(flagKey: string, defaultValue: T, context: EvaluationContext, logger: Logger): ResolutionDetails<T> { // code to evaluate an object } onContextChange?(oldContext: EvaluationContext, newContext: EvaluationContext): Promise<void> { // reconcile the provider's cached flags, if applicable } // implement with "new OpenFeatureEventEmitter()", and use "emit()" to emit events events?: ProviderEventEmitter<AnyProviderEvent> | undefined; initialize?(context?: EvaluationContext | undefined): Promise<void> { // code to initialize your provider } onClose?(): Promise<void> { // code to shut down your provider } } ``` > Built a new provider? [Let us know](https://github.com/open-feature/openfeature.dev/issues/new?assignees=&labels=provider&projects=&template=document-provider.yaml&title=%5BProvider%5D%3A+) so we can add it to the docs! ### Develop a hook To develop a hook, you need to create a new project and include the OpenFeature SDK as a dependency. This can be a new repository or included in [the existing contrib repository](https://github.com/open-feature/js-sdk-contrib) available under the OpenFeature organization. Implement your own hook by conforming to the [Hook interface](../shared/src/hooks/hook.ts). ```ts import type { Hook, HookContext, EvaluationDetails, FlagValue } from "@openfeature/web-sdk"; export class MyHook implements Hook { after(hookContext: HookContext, evaluationDetails: EvaluationDetails<FlagValue>) { // code that runs after flag values are successfully resolved from the provider } } ``` > Built a new hook? [Let us know](https://github.com/open-feature/openfeature.dev/issues/new?assignees=&labels=hook&projects=&template=document-hook.yaml&title=%5BHook%5D%3A+) so we can add it to the docs! ### Considerations When developing a library based on OpenFeature components, it's important to list the `@openfeature/web-sdk` as a `peerDependency` of your package. This is a general best-practice when developing JavaScript libraries that have dependencies in common with their consuming application. Failing to do this can result in multiple copies of the OpenFeature SDK in the consumer, which can lead to type errors, and broken singleton behavior. The `@openfeature/core` package itself follows this pattern: the `@openfeature/web-sdk` has a peer dependency on `@openfeature/core`, and uses whatever copy of that module the consumer has installed (note that NPM installs peers automatically unless `--legacy-peer-deps` is set, while yarn does not, and PNPM does so based on its configuration). When developing such libraries, it's NOT necessary to add a `peerDependency` on `@openfeature/core`, since the `@openfeature/web-sdk` establishes that dependency itself transitively.