Customize the JavaScript SDK logger v6+

The logger records information about your experiments to help you with debugging. You can customize where log information is sent and what kind of information is tracked.

Minimum SDK version

v6.0.0+

For versions 5.3.5 and below, see JavaScript (Browser) SDK or JavaScript (Node) SDK. See the SDK compatibility matrix documentation for a list of current SDK releases and the features they support.

Description

To enable logging for the Javascript SDK, create a logger using the createLoggerfactory function and pass the logger to createInstance.

import {
  createInstance,
  createPollingProjectConfigManager,
  createLogger,
  LogLevel,
  INFO
} from "@optimizely/optimizely-sdk";

const SDK_KEY = "YOUR_SDK_KEY";

const pollingConfigManager = createPollingProjectConfigManager({
  sdkKey: SDK_KEY,
});

const customLogHandler = {
  log: (level, message) => {
    switch (level) {
      case LogLevel.Info:
        // INFO log message
        console.info(message);
        break;
      
      case LogLevel.Debug:
        // DEBUG log message
        console.debug(message);
        break;

      case LogLevel.Warn:
        // WARNING log message
        console.warn(message);
        break;

      case LogLevel.Error:
        // ERROR log message
        console.error(message);
        break;
    }
  }
}

const logger = createLogger({
  level: INFO,
});

const loggerWithCustomHandler = createLogger({
  level: INFO,
  logHandler: customLogHandler,  
})

const optimizely = createInstance({
  projectConfigManager: pollingConfigManager,
  logger
});

To customize the logger instance, you could use following configuration:

Parameter	Type	Description
`level`	OpaqueLevelPreset	Level preset that can be used directly to create logger instance. Level presets can be imported from the package root.
`logHandler` optional	LogHandler	An interface that implements the log method. A custom `LogHandler`can be used to modify how log messages are handled (for example, storing in a file or sending to an external system). By default, a console log handler is used which prints the log message to the console.

Log level presets

The following table lists the log level presets available:

Log Level	Explanation
ERROR	Events that prevent feature flags or experiments from functioning correctly (for example, invalid datafile in initialization and invalid feature keys) are logged. You can take action to correct.
WARN	Events that do not prevent feature flags or experiments from functioning correctly, but can have unexpected outcomes (for example, future API deprecation, logger or error handler are not set properly) are logged.
INFO	Events of significance (for example, decision started, decision succeeded, tracking started, and tracking succeeded) are logged. This is helpful in showing the lifecycle of an API call.
DEBUG	Any information related to errors that can help you debug the issue (for example, the feature flag is not running, user is not included in the rollout) are logged.

They can be imported as follows:

import {
	DEBUG,
  INFO,
  WARN,
  ERROR
} from "@optimizely/optimizely-sdk";