@flipt-io/flipt-client v0.7.1

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

Supported Architectures

This SDK currently supports the following OSes/architectures:

• Linux x86_64
• Linux arm64
• MacOS x86_64
• MacOS arm64

Usage

In your Node 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.
// engine_opts is the second positional argument and is also optional, the structure is:
// {
//  "url": "http://localhost:8080",
//  "update_interval": 120,
//  "authentication": {
//    "client_token": "secret"
//  }
// }
//
// You can replace the url with where your upstream Flipt instance points to, the update interval for how long you are willing
// to wait for updated flag state, and the auth token if your Flipt instance requires it.
const fliptEvaluationClient = new FliptEvaluationClient();

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

console.log(variant);

Memory Management

Since TypeScript/JavaScript is a garbage collected language there is no concept of "freeing" memory. We have to allocate memory for the engine through the initialize_engine FFI call.

Make sure to call the close method on the FliptEvaluationClient class once you are done using it.

fliptEvaluationClient.close();

Potential Issues

Node v21+

If you are using Node v21 or higher, you'll likely run into issues with the ffi-napi library. This is due to the fact that ffi-napi does not seem to be compatible with Node v21+.

See: node-ffi-napi #267

To work around this issue you'll need to downgrade to Node v20 or lower. :(

We plan to look into alternative ffi libraries for node in the future. See #200

Vitest

If you are using this library in combination with vitest, you may run into segmentation fault issues. This is due to the fact that vitest does not work nicely with ffi-napi by default.

See the following issue for more information: vitest #2091: vitest will crash when using ffi-napi.

To work around this issue, it is recommended to run your tests with the --pool=forks flag.

See #169 for more information.