Flipt Client Node

The flipt-client-node library contains the JavaScript/TypeScript source code for the Flipt client-side evaluation client.

Installation

npm install @flipt-io/flipt-client

[!IMPORTANT] The latest version of the Flipt Node.js SDK does not currently work with Next.js App Router because Next.js App Router does not support WASM dependencies. See this issue for more information. Use version 0.9.0 of the SDK until this is resolved.

Usage

In your Node.js code you can import this client and use it as so:

import { FliptEvaluationClient } from '@flipt-io/flipt-client';

// namespace is the first positional argument and is optional here and will have a value of "default" if not specified.
// options is the second positional argument and is also optional, the structure is:
// {
//  "url": "http://localhost:8080",
//  "updateInterval": 120,
//  "authentication": {
//    "clientToken": "secret"
//  }
// }
//
// You can replace the url with where your upstream Flipt instance points to, the updateInterval for how long you are willing
// to wait for updated flag state, and the auth token if your Flipt instance requires it.
const fliptEvaluationClient = await FliptEvaluationClient.init('default', {
  url: 'http://localhost:8080',
  authentication: {
    clientToken: 'secret'
  }
});

const variant = fliptEvaluationClient.evaluateVariant('flag1', 'someentity', {
  fizz: 'buzz'
});

console.log(variant);

Initialization Arguments

The FliptEvaluationClient constructor accepts two optional arguments:

• namespace: The namespace to fetch flag state from. If not provided, the client will default to the default namespace.
• options: An instance of the ClientOptions type that supports several options for the client. The structure is:
  • url: The URL of the upstream Flipt instance. If not provided, the client will default to http://localhost:8080.
  • updateInterval: The interval (in seconds) in which to fetch new flag state. If not provided, the client will default to 120 seconds.
  • authentication: The authentication strategy to use when communicating with the upstream Flipt instance. If not provided, the client will default to no authentication. See the Authentication section for more information.
  • reference: The reference to use when fetching flag state. If not provided, reference will not be used.

Authentication

The FliptEvaluationClient supports the following authentication strategies:

• No Authentication (default)
• Client Token Authentication
• JWT Authentication

Custom Fetcher

The FliptEvaluationClient supports custom fetchers. This allows you to fetch flag state from a custom source or override HTTP headers.

The fetcher can be passed in as an argument to the FliptEvaluationClient initializer function.

const fliptEvaluationClient = await FliptEvaluationClient.init('default', {
  url: 'http://localhost:8080',
  authentication: {
    clientToken
  },
  fetcher: customFetcher
});

The fetcher is a function that takes an optional IFetcherOpts argument and returns a Promise that resolves to a Response object.

Timer Management

The FliptEvaluationClient class uses a timer to fetch new flag state at a regular interval.

Make sure to call the close method on the FliptEvaluationClient class once you are done using it to stop the timer and clean up resources.

fliptEvaluationClient.close();

State Management

The FliptEvaluationClient class pulls flag state from the Flipt instance at the url provided in the options object on instantiation.

This state is pulled from the Flipt instance on instantiation and every update_interval seconds thereafter.

To update the flag state manually, you can call the refresh method on the FliptEvaluationClient class.

[!NOTE] The refresh method returns a boolean indicating whether the flag state changed.

// Refresh the flag state
let changed = await fliptEvaluationClient.refresh();

if (changed) {
  // Do something
}

ETag Support

The default fetcher uses ETag HTTP headers to reduce overhead building and sending previously observed snapshots. This is useful in scenarios where the flag state is not frequently updated and you want to reduce the load on the server.

To disable ETag support, you can implement a custom fetcher that does not use ETags.

Development

WASM

This library uses a WebAssembly (WASM) layer to interact with the Flipt server. It is written in Rust and exposes a JavaScript API using the wasm-bindgen and wasm-pack tools. We wrap the built WASM layer in a JavaScript API to make it easier to use in a browser environment.

Prerequisites

• flipt-engine-wasm

Build

npm run build

Test

npm install
npm test

Contributing

Contributions are welcome! Please feel free to open an issue or submit a Pull Request.

License

This project is licensed under the MIT License.