Node.js SDK Reference

This topic describes how to use the Harness Feature Flags Node.js SDK for your Node.js application. For getting started quickly, you can use our sample code from the Node.js SDK README. You can also c

NOTE

This SDK is not currently supported on Harness Self-Managed Enterprise Edition (on premises).

This topic describes how to use the Harness Feature Flags Node.js SDK for your Node.js application.

For getting started quickly, you can use our sample code from the Node.js SDK README. You can also clone and run a sample application from the Node.js SDK GitHub Repository.

Before you begin

You should read and understand the following:

• Feature Flags Overview

• Getting Started with Feature Flags

• Client-Side and Server-Side SDKs

• Communication Strategy Between SDKs and Harness Feature Flags

Version

Latest SDK version can be found on GitHub Release Page

Requirements

To use this SDK, make sure you:

• Install Node.js version 12 or newer

• Download the SDK from our GitHub repository

• Create a Node.js application, or clone our sample application.

• Create a Feature Flag on the Harness Platform. If you are following along with the SDK README sample code, make sure your flag is called harnessappdemodarkmode

• Create an SDK key and make a copy of it

Install the SDK

Install using npm

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

Install using yarn

yarn add @harnessio/ff-nodejs-server-sdk

Initialize the SDK

To initialize the Node.js SDK, you need to:

1. Import the package.

2. Add your Server SDK Key to connect to your Harness Environment.

3. Add a Target that you want to Evaluate against a Feature Flag.

4. (Optional) Configure the SDK options. For more details on what features you can configure for this SDK, go to Configure the SDK.

Import the package

CommonJS

To import with CommonJS, use:

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

ES modules

To import with ES modules use:

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

Add the Server SDK Key

To connect to the correct Environment that you set up on the Harness Platform, you need to add the Server SDK Key from that Environment. Input the Client SDK Key into the API_KEY parameter, for example:

const client = new Client('sdkKey');

Add a Target

What is a Target?

Targets are used to control which users see which Variation of a Feature Flag, for example, if you want to do internal testing, you can enable the Flag for some users and not others. When creating a Target, you give it a name and a unique identifier. Often Targets are users but you can create a Target from anything that can be uniquely identified, such as an app or a machine.

For more information about Targets, go to Targeting Users With Flags.

To add a Target, build it and pass in arguments for the following:

Parameter	Description	Required?	Example
identifier	Unique ID for the Target.Read Regex requirements for Target names and identifiers below for accepted characters.	Required	identifier: 'HT_1'
name	Name for this Target. This does not have to be unique. Note: If you don’t provide a value, the name will be the same as the identifier.Read Regex requirements for Target names and identifiers below for accepted characters.	Optional Note: If you don't want to send a name, don't send the parameter. Sending an empty argument will cause an error.	name: 'Harness_Target_1'
attributes	Additional data you can store for a Target, such as email addresses or location.	Optional	attributes: {

Regex requirements for Target names and identifiers

Identifier

Regex: ^[A-Za-z0-9.@_-]*$ Must consist of only alphabetical characters, numbers, and the following symbols: . (period) @ (at sign) -(dash) _ (underscore)

The characters can be lowercase or uppercase but cannot include accented letters, for example Cafe_789.

Name Regex: ^[\\p{L}\\d .@_-]*$

Must consist of only alphabetical characters, numbers, and the following symbols: . (period) @ (at sign) -(dash) _ (underscore) (space)

The characters can be lowercase or uppercase and can include accented letters, for example Café_123.

For example:

const target = {  
    identifier: 'HT_1',  
    name: 'Harness_Target_1',  
    attributes: {  
       'email': '[e-mail]'  
    }  
  };

Configure the SDK

You can configure the following features of the SDK:

Name	Description	Default Value
baseUrl	The URL used to fetch Feature Flag Evaluations. When using the Relay Proxy, change this to: http://localhost:7000	https://config.ff.harness.io/api/1.0
eventsUrl	The URL for posting metrics data to the Feature Flag service. When using the Relay Proxy, change this to: http://localhost:7000	https://events.ff.harness.io/api/1.0
pollInterval	The interval in milliseconds that we poll for changes when you are using stream mode.	60 (seconds)
enableStream	Set to true to enable streaming mode.Set to false to disable streaming mode.	true
enableAnalytics	Set to true to enable analytics.Set to false to disable analytics.Note: When enabled, analytics data is posted every 60 seconds.	true

For example:

// Create Options  
const options = {  
  baseUrl: "http://localhost:7000",  
  eventsUrl: "http://localhost:7000"  
}

Complete the initialization

To complete the initialization:

1. Create an instance of the Feature Flag client and pass in the Server SDK Key and configuration options:

// Create client with options  
const client = new Client(apiKey, options);

1. Wait for the SDK to complete initialization and to fetch the Flag data:

await client.waitForInitialization();

Evaluate a Flag

Evaluating a Flag is when the SDK processes all Flag rules and returns the correct Variation of that Flag for the Target you provide.

If a matching Flag can’t be found, or the SDK can’t remotely fetch flags, the default value is returned.

There are different methods for the different Variation types and for each method you need to pass in:

• Identifier of the Flag you want to evaluate

• The Target object you want to evaluate against

• The default Variation

For example:

Evaluate a boolean Variation

function boolVariation(  
  identifier: string,  
  target: Target,  
  defaultValue: boolean = true,  
): Promise<boolean>;

Evaluate a string Variation

function stringVariation(  
  identifier: string,  
  target: Target,  
  defaultValue: boolean = '',  
): Promise<string>;

Evaluate a number Variation

function numberVariation(  
  identifier: string,  
  target: Target,  
  defaultValue: boolean = 1.0,  
): Promise<number>;

Evaluate a JSON Variation

function jsonVariation(  
  identifier: string,  
  target: Target,  
  defaultValue: boolean = {},  
): Promise<Record<string, unknown>>;

Listen for events

Register the event listener

You can listen for the following events:

• Event.READY - Indicates the SDK was successfully initialized.

• Event.FAILED - Indicates the SDK had thrown an error.

• Event.CHANGED - Indicates a Flag or Segment has been updated.

For example:

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

Close the event listener

To avoid unexpected behavior, when the listener isn't needed, turn it off.

To remove the functionReference listener for Event.READY, use:

off(Event.READY, functionReference);

To remove all listeners, use:

off(Event.READY);

If you call off() without parameters it will close the client.

Test your app is connected to Harness

When you receive a response showing the current status of your Feature Flag, go to the Harness Platform and toggle the Flag on and off. Then, check your app to verify if the Flag Variation displayed is updated with the Variation you toggled.

NOTE

The SDK must run for at least 60 seconds before it sends metrics. Please ensure metrics have not been disabled in the SDK.

Close the SDK client

In most applications, you won't need to close the SDK client.

However, you should close the SDK client if:

• Your application is about to terminate. Closing the client ensures that all associated resources are released.

• You have determined that you do not need to evaluate flags again in your application lifecycle.

IMPORTANT

The SDK does not evaluate flags after the client is closed.

To close the SDK, call the following function:

function close(): void;

Additional options

Configure your logger

You can provide your own logger to the SDK by 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()]  
  })  
});

Sample code for a Node.js application

Here is a sample code for using the SDK with a Node.js application:

  
  const pkg = require('ff-nodejs-server-sdk');  
const { Client } = pkg;  
  
const client = new Client('1c100d25-4c3f-487b-b198-3b3d01df5794', {  
  enableStream: true,  
  pollInterval: 2 * 60 * 1000 // two min pollInterval  
});  
  
setInterval(() => {  
  const target = {  
    identifier: 'harness',  
  };  
  const value = client.boolVariation('test', target, false);  
  console.log('Evaluation for flag test and target: ', value, target);  
}, 10000);

Troubleshooting

The SDK logs the following codes for certain lifecycle events, for example authentication, which can aid troubleshooting.

Code	Description	Log Level
1000	Successfully initialized	Info
1001	Failed to initialize due to authentication error	Error
1002	Failed to initialize due to a missing or empty API key	Error
1003	WaitForInitialization configuration option was provided and the SDK is waiting for initialization to finish	Info
2000	Successfully authenticated	Info
2001	Authentication failed with a non-recoverable error	Error
2002	Authentication failed and is retrying	Warn
2003	Authentication failed and max retries have been exceeded	Error
3000	SDK closing	Info
3001	SDK closed successfully	Info
4000	Polling service started	Info
4001	Polling service stopped	Info
5000	Streaming connected	Info
5001	Streaming disconnected	Warn
5002	Streaming event received	Debug
5003	Streaming disconnected and is retrying to connect	Info
5004	Streaming service stopped	Info
5005	Stream is still retrying to connect after 4 attempts	Warn
6000	Evaluation was successful	Debug
6001	Evaluation failed and the default value was returned	Info
7000	Metrics service has started	Info
7001	Metrics service has stopped	Info
7002	Metrics posting failed	Warn
7003	Metrics posting success	Debug
7004	Metrics max target size exceeded	Warn
7007	Metrics max evaluation size reached	Warn