README

Harness Feature Flags Server SDK for NodeJS

Before you Begin

Harness Feature Flags (FF) is a feature management solution that enables users to change the software’s functionality, without deploying new code. FF uses feature flags to hide code or behaviours without having to ship new versions of the software. A feature flag is like a powerful if statement.

For more information, see https://harness.io/products/feature-flags/

To sign up, https://app.harness.io/auth/#/signup/

Getting Started

Setup

npm install @harnessio/ff-nodejs-server-sdk

Import the package (CommonJS)

const { Client } = require('@harnessio/ff-nodejs-server-sdk');

Import the package (ES modules)

import { Client } from '@harnessio/ff-nodejs-server-sdk';

Initialize

This is the most simple way to initialize SDK using only a server type key

const client = new Client('your server type SDK key');

Advanced initialization can be done using options

const client = new Client('your server type SDK key', {
  enableStream: false,
});

Define a target

const target = {
  identifier: 'harness',
  name: 'Harness',
  attributes: {}
};

Evaluate the flag with default value set to false

const value = await client.boolVariation('test', target, false);

Shutting down SDK

client.close();

Avaialable public methods

function boolVariation(
  identifier: string,
  target: Target,
  defaultValue: boolean = true,
): Promise<boolean>;
function stringVariation(
  identifier: string,
  target: Target,
  defaultValue: boolean = '',
): Promise<string>;
function numberVariation(
  identifier: string,
  target: Target,
  defaultValue: boolean = 1.0,
): Promise<number>;
function jsonVariation(
  identifier: string,
  target: Target,
  defaultValue: boolean = {},
): Promise<Record<string, unknown>>;
function close(): void;

Avaialable options

baseUrl: string;             // baseUrl is where the flag configurations are located
eventsUrl: string;           // eventsUrl is where we send summarized target events
pollInterval: number;        // pollInterval (default 60s)
eventsSyncInterval: number;  // Metrics push event (default 60s)
enableStream: boolean;       // enable server sent events
enableAnalytics: boolean;    // enable analytics
cache: KeyValueStore;        // set custom cache (default lru cache)
store: AsyncKeyValueStore;   // set custom persistent store (default file store)
logger: Logger;              // set logger (default console)

Singleton example

import CfClient from '@harnessio/ff-nodejs-server-sdk';

CfClient.init('your server type SDK key');

const FLAG_KEY = 'test_bool';
const target = {
  identifier: 'harness',
  name: 'Harness',
  attributes: {}
};
const defaultValue = false;

setInterval(async() => {
    const value = await CfClient.boolVariation(FLAG_KEY, target, defaultValue);
    console.log("Evaluation for flag test and target none: ", value);
}, 10000);

Wait for initialization example

const { Client } = require('@harnessio/ff-nodejs-server-sdk');

console.log('Starting application');
const client = new Client('1c100d25-4c3f-487b-b198-3b3d01df5794');
client
  .waitForInitialization()
  .then(() => {
    setInterval(async () => {
      const target = {
        identifier: 'harness',
      };
      const value = await client.boolVariation('test', target, false);
      console.log('Evaluation for flag test and target: ', value, target);
    }, 10000);

    console.log('Application started');
  })
  .catch((error) => {
    console.log('Error', error);
  });

Listening on events

You can listen on these events:

Event.READY - SDK successfully initialized
Event.FAILED - SDK throws an error
Event.CHANGED - any new version of flag or segment triggers this event, if segment is changed then it will find all flags with segment match operator

Methods:

on(Event.READY, () => {
  console.log('READY');
});

on(Event.FAILED, () => {
  console.log('FAILED');
});

on(Event.CHANGED, (identifier) => {
  console.log('Changed', identifier);
});

and if you want to remove the functionReference listener for Event.READY:

off(Event.READY, functionReference);

or if you want to remove all listeners on Event.READY:

off(Event.READY);

or if you call off() without params it will close the client.

All events are applicable to off() function.

License

Licensed under the APLv2.

Usage no npm install needed!