VWO Node/JavaScript SDK for Feature Management and Experimentation
npm install vwo-fme-node-sdk
[](http://img.badgesize.io/wingify/vwo-fme-node-sdk/master/dist/client/vwo-fme-javascript-sdk.min.js?compression=gzip&color=blue&style=for-the-badge)
The VWO Feature Management and Experimentation SDK (VWO FME Node SDK) enables Node.js and JavaScript developers to integrate feature flagging and experimentation into their applications. This SDK provides full control over feature rollout, A/B testing, and event tracking, allowing teams to manage features dynamically and gain insights into user behavior.
- Node.js v12 or later
Install the SDK via npm or yarn:
``bashvia npm
npm install vwo-fme-node-sdk --save
Basic Usage Example
The following example demonstrates initializing the SDK with a VWO account ID and SDK key, setting a user context, checking if a feature flag is enabled, and tracking a custom event.
javascript
const { init } = require('vwo-fme-node-sdk');// Initialize VWO client
(async function () {
const vwoClient = await init({
accountId: '123456',
sdkKey: '32-alpha-numeric-sdk-key',
});
// Check if feature is enabled for user
const userContext = { id: 'unique_user_id' };
const feature = await vwoClient.getFlag('feature_key', userContext);
if (feature.isEnabled()) {
console.log('Feature is enabled!');
// Get feature variable
const value = feature.getVariable('feature_variable', 'default_value');
console.log('Variable value:', value);
}
// Track an event
vwoClient.trackEvent('event_name', userContext);
})();
`The SDK includes TypeScript type definitions for better type safety and IDE support. Here's how to use the SDK with TypeScript:
typescript
import { init, IVWOClient, IVWOOptions, Flag } from 'vwo-fme-node-sdk';
// Example of using IVWOOptions for type-safe configuration
const options: IVWOOptions = {
accountId: '123456',
sdkKey: '32-alpha-numeric-sdk-key',
};// Example of using IVWOClient for type-safe client usage
const vwoClient: IVWOClient = await init(options);
// Example of using Flag interface for type-safe flag handling
const flag: Flag = await vwoClient.getFlag('feature-key', { id: 'user-123' });
const isEnabled: boolean = flag.isEnabled();
const stringVariable: string = flag.getVariable('variable_key', 'default_value');
const booleanVariable: boolean = flag.getVariable('variable_key', true);
const numberVariable: number = flag.getVariable('variable_key', 10);
`Advanced Configuration Options
To customize the SDK further, additional parameters can be passed to the
API. Here's a table describing each option:| Parameter | Description | Required | Type | Example |
| ---------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------ | -------- | --------------------------------------------- |
|
accountId | VWO Account ID for authentication. | Yes | String | '123456' |
| sdkKey | SDK key corresponding to the specific environment to initialize the VWO SDK Client. You can get this key from VWO Application. | Yes | String | '32-alpha-numeric-sdk-key' |
| pollInterval | Time interval for fetching updates from VWO servers (in milliseconds). | No | Number | 60000 |
| gatewayService | An object representing configuration for integrating VWO Gateway Service. | No | Object | see Gateway section |
| storage | Custom storage connector for persisting user decisions and campaign data. | No | Object | See Storage section |
| clientStorage | Browser storage configuration for persisting user data in browser environments. | No | Object | See Client Storage section |
| logger | Toggle log levels for more insights or for debugging purposes. You can also customize your own transport in order to have better control over log messages. | No | Object | See Logger section |
| shouldWaitForTrackingCalls | Ensures tracking calls complete before resolving promises, useful for edge computing environments like Cloudflare Workers | No | Boolean | true |
| integrations | A callback function that receives data which can be pushed to any external tool that you need to integrate with. | No | Object | See Integrations |
| batchEventData | Configuration for batch event processing to optimize network requests | No | Object | See Batch Events section |
| retryConfig | Configuration for network request retry behavior and exponential backoff strategy | No | Object | See Retry Config section |
| edgeConfig | Configuration for edge/serverless environment optimizations (e.g., Cloudflare Workers) | No | Object | See Edge Config section |Refer to the official VWO documentation for additional parameter details.
$3
The
context object uniquely identifies users and is crucial for consistent feature rollouts. A typical context includes an id for identifying the user. It can also include other attributes that can be used for targeting and segmentation, such as customVariables, userAgent and ipAddress.#### Parameters Table
The following table explains all the parameters in the
context object:| Parameter | Description | Required | Type | Example |
| ----------------- | -------------------------------------------------------------------------- | ------------ | -------- | --------------------------------- |
|
id | Unique identifier for the user. | Yes | String | 'unique_user_id' |
| customVariables | Custom attributes for targeting. | No | Object | { age: 25, location: 'US' } |
| userAgent | User agent string for identifying the user's browser and operating system. | No | String | 'Mozilla/5.0 ... Safari/537.36' |
| ipAddress | IP address of the user. | No | String | '1.1.1.1' |#### Example
`javascript
const userContext = {
id: 'unique_user_id',
customVariables: { age: 25, location: 'US' },
userAgent:
'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/130.0.0.0 Safari/537.36',
ipAddress: '1.1.1.1',
};
`$3
The SDK provides automatic session management capabilities to enable seamless integration with VWO's web client testing campaigns. Session IDs are automatically generated and managed to connect server-side feature flag decisions with client-side user sessions.
#### Automatic Session ID Generation
Session IDs are automatically generated using Unix timestamps when not explicitly provided in the context. This ensures consistent session tracking across all feature flag evaluations and event tracking.
#### Session ID Access
You can access and manage session IDs through the following methods:
- Get Session ID from Flag: Use
to retrieve the session ID used for a specific feature flag evaluation
- Set Custom Session ID: Include sessionId in your context object to use a custom session ID (useful for matching web client sessions)#### Example Usage
`javascript
// Session ID is automatically generated if not provided
const context = { id: 'user-123' };
const flag = await vwoClient.getFlag('feature-key', context);// Access the session ID to pass to web client for session recording
const sessionId = flag.getSessionId();
console.log('Session ID for web client:', sessionId);
`You can also explicitly set a session ID to match web client session
javascript
const context = {
id: 'user-123',
sessionId: 1697123456, // Custom session ID matching web client
};
const flag = await vwoClient.getFlag('feature-key', context);
`This enhancement enables seamless integration between server-side feature flag decisions and client-side session recording, allowing for comprehensive user behavior analysis across both server and client environments.
$3
Feature Flags serve as the foundation for all testing, personalization, and rollout rules within FME.
To implement a feature flag, first use the
API to retrieve the flag configuration.
The getFlag API provides a simple way to check if a feature is enabled for a specific user and access its variables. It returns a feature flag object that contains methods for checking the feature's status and retrieving any associated variables.| Parameter | Description | Required | Type | Example |
| ------------ | ---------------------------------------------------------------- | -------- | ------ | -------------------- |
|
featureKey | Unique identifier of the feature flag | Yes | String | 'new_checkout' |
| context | Object containing user identification and contextual information | Yes | Object | { id: 'user_123' } |Example usage:
`javascript
const featureFlag = await vwoClient.getFlag('feature_key', { id: 'unique_user_id' });
const isEnabled = featureFlag.isEnabled();if (isEnabled) {
console.log('Feature is enabled!');
// Get and use feature variable with type safety
const variableValue = featureFlag.getVariable('feature_variable', 'default_value');
console.log('Variable value:', variableValue);
} else {
console.log('Feature is not enabled!');
}
`$3
Feature flags can be enhanced with connected metrics to track key performance indicators (KPIs) for your features. These metrics help measure the effectiveness of your testing rules by comparing control versus variation performance, and evaluate the impact of personalization and rollout campaigns. Use the
API to track custom events like conversions, user interactions, and other important metrics:| Parameter | Description | Required | Type | Example |
| ----------------- | ---------------------------------------------------------------------- | -------- | ------ | ---------------------- |
|
eventName | Name of the event you want to track | Yes | String | 'purchase_completed' |
| context | Object containing user identification and other contextual information | Yes | Object | { id: 'user_123' } |
| eventProperties | Additional properties/metadata associated with the event | No | Object | { amount: 49.99 } |Example usage:
`javascript
vwoClient.trackEvent('event_name', { id: 'unique_user_id' }, { amount: 49.99 });
`See Tracking Conversions documentation for more information.
$3
User attributes provide rich contextual information about users, enabling powerful personalization. The
method provides a simple way to associate these attributes with users in VWO for advanced segmentation. Here's what you need to know about the method parameters:| Parameter | Description | Required | Type | Example |
| ---------------- | ---------------------------------------------------------------------- | -------- | ------ | ----------------------- |
|
attributeKey | The unique identifier/name of the attribute you want to set | Yes | String | 'plan_type' |
| attributeValue | The value to be assigned to the attribute | Yes | Any | 'premium', 25, etc. |
| context | Object containing user identification and other contextual information | Yes | Object | { id: 'user_123' } |Example usage:
`javascript
vwoClient.setAttribute('attribute_name', 'attribute_value', { id: 'unique_user_id' });
`See Pushing Attributes documentation for additional information.
$3
The
is an optional parameter that allows the SDK to automatically fetch and update settings from the VWO server at specified intervals. The polling interval can be configured in three ways:1. Set via SDK options: If
pollInterval is specified in the initialization options (must be >= 1000 milliseconds), that interval will be used
2. VWO Application Settings: If configured in your VWO application settings, that interval will be used
3. Default Fallback: If neither of the above is set, a 10 minute (600,000 milliseconds) polling interval is usedSetting this parameter ensures your application always uses the latest configuration by periodically checking for and applying any updates.
`javascript
const vwoClient = await init({
accountId: '123456',
sdkKey: '32-alpha-numeric-sdk-key',
pollInterval: 60000,
});
`$3
The VWO FME Gateway Service is an optional but powerful component that enhances VWO's Feature Management and Experimentation (FME) SDKs. It acts as a critical intermediary for pre-segmentation capabilities based on user location and user agent (UA). By deploying this service within your infrastructure, you benefit from minimal latency and strengthened security for all FME operations.
#### Why Use a Gateway?
The Gateway Service is required in the following scenarios:
- When using pre-segmentation features based on user location or user agent.
- For applications requiring advanced targeting capabilities.
- It's mandatory when using any thin-client SDK (e.g., Go).
#### How to Use the Gateway
The gateway can be customized by passing the
parameter in the init configuration.`javascript
const vwoClient = await init({
accountId: '123456',
sdkKey: '32-alpha-numeric-sdk-key',
gatewayService: {
url: 'https://custom.gateway.com',
},
});
`Refer to the Gateway Documentation for further details.
$3
User aliasing lets you associate an existing user ID with an alternate ID (alias) so future evaluations and tracking use a unified identity across systems.
Requirements:
- Gateway must be configured.
- Aliasing must be enabled during initialization:
Initialization example:
javascript
const vwoClient = await init({
accountId: '123456',
sdkKey: '32-alpha-numeric-sdk-key',
isAliasingEnabled: true,
gatewayService: { url: 'https://custom.gateway.com' },
});
`Usage examples:
javascript
// Using context object
const success1 = await vwoClient.setAlias({ id: 'user-123' }, 'alias-abc');// Using direct userId
const success2 = await vwoClient.setAlias('user-123', 'alias-abc');
`Behavior and validations:
- Returns
on success, false otherwise
- Requires aliasing to be enabled and gateway configured
- aliasId must be a non-empty string (not an array); it is trimmed before use
- For context usage, context.id must be a non-empty string (not an array); it is trimmed before use
- userId and aliasId cannot be the same$3
The SDK operates in a stateless mode by default, meaning each
getFlag call triggers a fresh evaluation of the flag against the current user context.To optimize performance and maintain consistency, you can implement a custom storage mechanism by passing a
storage parameter during initialization. This allows you to persist feature flag decisions in your preferred database system (like Redis, MongoDB, or any other data store).Key benefits of implementing storage:
- Improved performance by caching decisions
- Consistent user experience across sessions
- Reduced load on your application
The storage mechanism ensures that once a decision is made for a user, it remains consistent even if campaign settings are modified in the VWO Application. This is particularly useful for maintaining a stable user experience during A/B tests and feature rollouts.
`javascript
class StorageConnector extends StorageConnector {
constructor() {
super();
} /**
* Get data from storage
* @param {string} featureKey
* @param {string} userId
* @returns {Promise
/**
* Set data in storage
* @param {object} data
*/
async set(data) {
// Set data corresponding to a featureKey and user ID
// Use data.featureKey and data.userId to store the above data for a specific feature and a user
}
}
const vwoClient = await init({
accountId: '123456',
sdkKey: '32-alpha-numeric-sdk-key',
storage: StorageConnector,
});
`$3
In browser environments, the SDK automatically uses
to persist user data. You can customize this behavior using the clientStorage option:`javascript
const vwoClient = await init({
accountId: '123456',
sdkKey: '32-alpha-numeric-sdk-key',
clientStorage: {
key: 'vwo_data', // defaults to vwo_fme_data
provider: sessionStorage, // defaults to localStorage
isDisabled: false, // defaults to false, set to true to disable storage
},
});
`| Parameter | Description | Required | Type | Default |
| ------------- | ------------------------------------------------- | ------------ | -------- | ---------------- |
|
| Key used to store data in browser storage | No | String | 'vwo_fme_data' |
| provider | Storage provider (localStorage or sessionStorage) | No | Object | localStorage |
| isDisabled | Disable browser storage completely | No | Boolean | false |Note: This feature is only applicable in browser environments. In Node.js environments, you should continue using the
storage option for custom storage implementations.$3
VWO by default logs all
ERROR level messages to your server console.
To gain more control over VWO's logging behaviour, you can use the logger parameter in the init configuration.| Parameter | Description | Required | Type | Example |
| ------------- | -------------------------------------- | ------------ | -------- | --------------------- |
|
level | Log level to control verbosity of logs | Yes | String | DEBUG |
| prefix | Custom prefix for log messages | No | String | 'CUSTOM LOG PREFIX' |
| transport | Custom logger implementation | No | Object | See example below |#### Example 1: Set log level to control verbosity of logs
`javascript
const vwoClient1 = await init({
accountId: '123456',
sdkKey: '32-alpha-numeric-sdk-key',
logger: {
level: 'DEBUG',
},
});
`#### Example 2: Add custom prefix to log messages for easier identification
javascript
const vwoClient2 = await init({
accountId: '123456',
sdkKey: '32-alpha-numeric-sdk-key',
logger: {
level: 'DEBUG',
prefix: 'CUSTOM LOG PREFIX',
},
});
`#### Example 3: Implement custom transport to handle logs your way
The
parameter allows you to implement custom logging behavior by providing your own logging functions. You can define handlers for different log levels (debug, info, warn, error, trace) to process log messages according to your needs.For example, you could:
- Send logs to a third-party logging service
- Write logs to a file
- Format log messages differently
- Filter or transform log messages
- Route different log levels to different destinations
The transport object should implement handlers for the log levels you want to customize. Each handler receives the log message as a parameter.
`javascript
const vwoClient3 = await init({
accountId: '123456',
sdkKey: '32-alpha-numeric-sdk-key',
logger: {
transport: {
level: 'INFO',
log: (level, message) => {
// your custom implementation here
},
},
},
});
`For multiple transports you can use the
parameter. For example:`javascript
const vwoClient3 = await init({
accountId: '123456',
sdkKey: '32-alpha-numeric-sdk-key',
logger: {
transports: [
{
level: 'INFO',
log: (level, message) => {
// your custom implementation here
},
},
{
level: 'ERROR',
log: (level, message) => {
// your custom implementation here
},
},
],
},
});
`$3
VWO FME SDKs provide seamless integration with third-party tools like analytics platforms, monitoring services, customer data platforms (CDPs), and messaging systems. This is achieved through a simple yet powerful callback mechanism that receives VWO-specific properties and can forward them to any third-party tool of your choice.
javascript
const vwoClient = await vwo.init({
sdkKey: '32-alpha-numeric-sdk-key', //replace with the SDK key for your environment
accountId: '123456', //replace with your VWO account ID
integrations: {
callback(properties) {
// your custom implementation here
},
},
});
`$3
The
is an optional parameter that allows you to control whether the SDK should wait for tracking calls to complete before resolving promises. When enabled, tracking API calls will wait for the server response before resolving.This is particularly useful for edge computing environments like Cloudflare Workers, where it ensures that tracking calls complete before resolving the promise.
`javascript
const vwoClient = await init({
accountId: '123456',
sdkKey: '32-alpha-numeric-sdk-key',
shouldWaitForTrackingCalls: true,
});
`$3
The
configuration allows you to optimize network requests by batching multiple events together. This is particularly useful for high-traffic applications where you want to reduce the number of API calls.| Parameter | Description | Required | Type | Default |
| --------------------- | ----------------------------------------------------------------------- | ------------ | -------- | ----------- |
|
requestTimeInterval | Time interval (in seconds) after which events are flushed to the server | No | Number | 600 |
| eventsPerRequest | Maximum number of events to batch together before sending to the server | No | Number | 100 |
| flushCallback | Callback function to be executed after events are flushed | No | Function | See example |Example usage:
`javascript
const vwoClient = await init({
accountId: '123456',
sdkKey: '32-alpha-numeric-sdk-key',
batchEventData: {
requestTimeInterval: 60, // Flush events every 60 seconds
eventsPerRequest: 100, // Send up to 100 events per request
flushCallback: (error, events) => {
console.log('Events flushed successfully');
// custom implementation here
},
},
});
`You can also manually flush events using the
method:`javascript
vwoClient.flushEvents();
`$3
The
parameter allows you to customize the retry behavior for network requests. This is particularly useful for applications that need to handle network failures gracefully with exponential backoff strategies.| Parameter | Description | Required | Type | Default | Validation |
| ------------------- | --------------------------------------------------------- | ------------ | -------- | ----------- | ----------------------------------- |
|
shouldRetry | Whether to enable automatic retry on network failures | No | Boolean | true | Must be a boolean value |
| maxRetries | Maximum number of retry attempts before giving up | No | Number | 3 | Must be a non-negative integer >= 1 |
| initialDelay | Initial delay (in seconds) before the first retry attempt | No | Number | 2 | Must be a non-negative integer >= 1 |
| backoffMultiplier | Multiplier for exponential backoff between retry attempts | No | Number | 2 | Must be a non-negative integer >= 2 |#### How Retry Logic Works
The SDK implements an exponential backoff strategy for retrying failed network requests:
1. Initial Request: The SDK attempts the initial network request
2. On Failure: If the request fails and
shouldRetry is true, the SDK waits for initialDelay seconds
3. Exponential Backoff: For subsequent retries, the delay is calculated as: initialDelay × (backoffMultiplier ^ attempt)
4. Maximum Attempts: The SDK will retry up to times before giving up#### Example Usage
`javascript
const vwoClient = await init({
accountId: '123456',
sdkKey: '32-alpha-numeric-sdk-key',
retryConfig: {
shouldRetry: true, // Enable retries
maxRetries: 5, // Retry up to 5 times
initialDelay: 3, // Wait 3 seconds before first retry
backoffMultiplier: 2, // Double the delay for each subsequent retry
},
});
`With this configuration, the retry delays would be:
- 1st retry: 3 seconds (3 × 2^0)
- 2nd retry: 6 seconds (3 × 2^1)
- 3rd retry: 12 seconds (3 × 2^2)
- 4th retry: 24 seconds (3 × 2^3)
- 5th retry: 48 seconds (3 × 2^4)
$3
The
option enables edge/serverless environment optimizations. This configuration should only be passed in serverless environments (e.g., Cloudflare Workers). When used in Cloudflare environments, events are automatically flushed using ctx.waitUntil(vwoClient.flushEvents()); to ensure proper event tracking after execution completes.| Parameter | Description | Required | Type | Default |
| ---------------------------- | --------------------------------------------------------- | ------------ | -------- | ----------- |
|
shouldWaitForTrackingCalls | Ensures tracking calls complete before resolving promises | Yes | Boolean | false |#### Example Usage
`javascript
const vwoClient = await init({
accountId: '123456',
sdkKey: '32-alpha-numeric-sdk-key',
edgeConfig: {
shouldWaitForTrackingCalls: true,
},
});// at the end flush all events
await vwoClient.flushEvents();
`Note: In Cloudflare, use
to ensure all events flush.$3
The
getUUID method allows you to generate a UUID that gets stored on VWO by providing a userId and accountId. This UUID is generated using a deterministic algorithm based on the user and account identifiers, ensuring consistent UUID generation for the same user-account combination.#### Parameters
| Parameter | Description | Required | Type | Example |
| ------------- | ---------------------------------- | ------------ | -------- | ------------ |
|
userId | The unique identifier for the user | Yes | String | 'user-123' |
| accountId | The account ID | Yes | String | '123456' |#### Return Value
Returns a UUID string formatted without dashes and in uppercase (e.g.,
'CC25A368ADA0542699EAD62489811105').#### Example Usage
`javascript
const { getUUID } = require('vwo-fme-node-sdk');// Generate UUID for a user
const userId = 'user-123';
const accountId = '123456';
const uuid = getUUID(userId, accountId);
console.log('Generated UUID:', uuid);
// Output: Generated UUID: CC25A368ADA0542699EAD62489811105
`$3
The SDK supports creating multiple instances, each with its own isolated configuration, services, and state. This is particularly useful when you need to work with multiple VWO accounts or environments simultaneously.
javascript
const { init } = require('vwo-fme-node-sdk');// Initialize multiple VWO clients with different account IDs and SDK keys
(async function () {
// First instance for production environment
const vwoClientProd = await init({
accountId: '123456',
sdkKey: '32-alpha-numeric-sdk-key-prod',
});
// Second instance for staging environment
const vwoClientStaging = await init({
accountId: '789012',
sdkKey: '32-alpha-numeric-sdk-key-staging',
});
// Each instance operates independently with its own settings and state
const userContext = { id: 'unique_user_id' };
// Use production client
const prodFeature = await vwoClientProd.getFlag('feature_key', userContext);
console.log('Production feature enabled:', prodFeature.isEnabled());
// Use staging client
const stagingFeature = await vwoClientStaging.getFlag('feature_key', userContext);
console.log('Staging feature enabled:', stagingFeature.isEnabled());
})();
`Each SDK instance maintains its own:
- Settings and configuration
- Services (storage, logger, network layer, etc.)
- Utils and helper functions
- State and cached data
This ensures complete isolation between instances, allowing you to safely use multiple VWO accounts or environments in the same application without any interference.
$3
The version history tracks changes, improvements, and bug fixes in each version. For a full history, see the CHANGELOG.md.
Development and Testing
$3
bash
yarn install
`$3
bash
yarn build
`$3
bash
production tests
yarn run test:proddevelopment tests
yarn run test:dev
``We welcome contributions to improve this SDK! Please read our contributing guidelines before submitting a PR.
Our Code of Conduct outlines expectations for all contributors and maintainers.
Copyright 2024-2026 Wingify Software Pvt. Ltd.