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further_reading.md

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Configuration Options

The following configuration options are available to control the behaviour of the SDK. You can provide options by passing them in when the client is created e.g.

// Create Options
const options = {
  baseUrl: "http://www.alternative-url.com",
  eventsUrl: "http://www.alternative-url.com"
}

// Create client with options
const client = new Client(apiKey, options);
Name Description default
baseUrl the URL used to fetch feature flag evaluations. You should change this when using the Feature Flag proxy to http://localhost:7000 https://config.ff.harness.io/api/1.0
eventsUrl the URL used to post metrics data to the feature flag service. You should change this when using the Feature Flag proxy to http://localhost:7000 https://events.ff.harness.io/api/1.0
pollInterval when running in stream mode, the interval in seconds that we poll for changes. 60
enableStream Enable streaming mode. true
enableAnalytics Enable analytics. Metrics data is posted every 60s true

Logging Configuration

You can provide your own logger to the SDK, passing it in as a config option. The following example creates an instance of the winston logger, sets the level to DEBUG and passes it to the client.

const winston = require('winston')

// Create client with logger
const client = new Client(apiKey, {
  logger: new winston.createLogger({
    level: 'debug',
    transports: [new winston.transports.Console()]
  })
});

Importing and Initializing the 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();

Available 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;

Available 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)
axiosTimeout: number;        // set timeout for requests to Harness (default 30s)

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.