Javascript / Typescript SDK usage

This page describes how to use the OpenFeature Javascript web SDK for your client application.

About this provider

GO Feature Flag provider allows you to connect to your GO Feature Flag instance with the @openfeature/web-sdk.

The main difference between this provider and @openfeature/go-feature-flag-provider is that it uses a static evaluation context. This provider is more sustainable for client-side implementation.

If you want to know more about this pattern, I encourage you to read this blog post.

Install the provider

npm install @openfeature/go-feature-flag-web-provider @openfeature/web-sdk

How to use the provider?

const evaluationCtx: EvaluationContext = {
  targetingKey: 'user-key',
  email: 'john.doe@gofeatureflag.org',
  name: 'John Doe',
};

const goFeatureFlagWebProvider = new GoFeatureFlagWebProvider({
  endpoint: endpoint,
  // ...
}, logger);

await OpenFeature.setContext(evaluationCtx); // Set the static context for OpenFeature
OpenFeature.setProvider(goFeatureFlagWebProvider); // Attach the provider to OpenFeature
const client = await OpenFeature.getClient();

// You can now use the client to use your flags
if(client.getBooleanValue('my-new-feature', false)){
    //...
}

// You can add handlers to know what happen in the provider
client.addHandler(ProviderEvents.Ready, () => { ... });
client.addHandler(ProviderEvents.Error, () => { //... });
client.addHandler(ProviderEvents.Stale, () => { //... });
client.addHandler(ProviderEvents.ConfigurationChanged, () => { //... });

Limit the flags to evaluate

By default, the provider will fetch all the flags configured in the GO Feature Flag server to be ready to evaluate them. If you know in advance, what are the flags you will evaluate in your application, you can specify the list of flags to evaluate in the context.

You need to add in the evaluation context the restricted key gofeatureflag.flagList with the list of flags you want to evaluate.

OpenFeature.setContext({
  // ...
  gofeatureflag: {
    flagList: ['flag1', 'flag2']
  }
});

await OpenFeature.setContext(evaluationCtx);

By setting the gofeatureflag.flagList key in the context, the provider will only fetch the flags specified in the list.

warning

When limiting the flags to evaluate, if you try to evaluate a flag not in the list, the provider will return the default value with the error FLAG_NOT_FOUND.

Available options

Option name	Type	Default	Description
endpoint	string		endpoint is the URL where your GO Feature Flag server is located.
apiTimeout	number	0 = no timeout	(optional) timeout is the time in millisecond we wait for an answer from the server.
apiKey	string		(optional) If GO Feature Flag is configured to authenticate the requests, you should provide an API Key to the provider. Please ask the administrator of the relay proxy to provide an API Key.
websocketRetryInitialDelay	number	100	(optional) initial delay in millisecond to wait before retrying to connect the websocket
websocketRetryDelayMultiplier	number	2	(optional) multiplier of websocketRetryInitialDelay after each failure (example: 1st connection retry will be after 100ms, second after 200ms, third after 400ms ...)
websocketMaxRetries	number	10	(optional) maximum number of retries before considering the websocket unreachable

Reconnection

If the connection to the GO Feature Flag instance fails, the provider will attempt to reconnect with an exponential back-off. The websocketMaxRetries can be specified to customize reconnect behavior.

Event streaming

The GoFeatureFlagWebProvider receives events from GO Feature Flag with changes. Combined with the event API in the web SDK, this allows for subscription to flag value changes in clients.

client.addHandler(ProviderEvents.ConfigurationChanged, (ctx: EventDetails) => {
  // do something when the configuration has changed.
  // ctx.flagsChanged contains the list of changed flags.
});

Contribute to the provider

You can find the source of the provider in the open-feature/js-sdk-contrib repository.