Configure the Logger

Every backend application relies on some kind of logs to debug it. The VWO SDK logger logs information about your running campaigns to help you with debugging. You can customize what kind of logs you need and where to send these, that is, you can write your own logger implementation to write the logs on some file, database, or some third-party logging service.



For the production environment, we recommend that you pass in your custom logger implementation while creating a VWO client instance.


A logger is a JSON object, which has the following keys:

Key nameTypeDefault (if any)Description
logFunctionDo NOT create this key for default logger implementation.Custom implementation of logger.
levelStringERROR, that is, vwoSDK.logging.LogLevelEnum.ERRORThe kind of logs that are needed.

Log Levels

Log LevelDescription
ERROR The events that prevent campaigns from functioning properly (for example, invalid settingsFile while initializing the VWO SDK, invalid campaign keys, or goal identifiers) are logged.
WARNING The events that don't prevent campaigns from functioning correctly, but can have unexpected outcomes (for example, future API deprecation) are logged.
INFO The events which are useful and provide a certain level of information (for example, activate started, bucket value assigned, part of a campaign, tracking user, conversion succeeded, and others) are logged. This depicts the flow of the API method used.
DEBUG Any kind of useful information that can help VWO debug the issue in case of unexpected behavior (for example, a user is not in a campaign, bucket value assigned, hash value assigned, and stored User Storage Service used, and others) are logged.

To filter these log levels while writing your own logger implementation, use the Enum provided to you by VWO SDKs.

var vwoSDK = require('vwo-node-sdk');

// debug level
var logDebugLevel = vwoSDK.logging.LogLevelEnum.DEBUG:

// info level
var logInfoLevel = vwoSDK.logging.LogLevelEnum.INFO:

// warn level
var logWarnLevel = vwoSDK.logging.LogLevelEnum.WARN:

// error level
var logErrorLevel = vwoSDK.logging.LogLevelEnum.ERROR:

See the code example below on how to use these appropriately.


var vwoSDK = require('vwo-node-sdk');

var customLoggingConfig = {
  logger: {
    log: (level, message) => {
      switch (level) {
        case vwoSDK.logging.LogLevelEnum.DEBUG:
        case vwoSDK.logging.LogLevelEnum.INFO:
        case vwoSDK.logging.LogLevelEnum.ERROR:
        case vwoSDK.logging.LogLevelEnum.WARN:

      // Write below the logic to write logs to a file or pass onto other services, if required
      // Code goes here...
  level: vwoSDK.logging.LogLevelEnum.DEBUG

vwoClientInstance = vwoSDK.createInstance({
  settingsFile: settingsFile, // required
  logging: customLoggingConfig // required only when custom logger implementation is required