# About Migrating to TD Javascript SDK Version 4.2.1

This article describes how to migrate v2 or v3 web tracking modules to v4.

## What's new in TD Javascript SDK 4.0

The following changes have been made to td-js-sdk v4:

* The SDK now uses the new "records.in" ingest base URL. For example, US developers will configure the ingest endpoint to "https://us01.records.in.treasuredata.com". (For a list of new ingest endpoints by region, see [Treasure Data Sites and baseURLs](https://api-docs.treasuredata.com/en/overview/aboutendpoints/).)
* The SDK no longer populates these values:
  * td_browser
  * td_browser_version
  * td_os
  * td_os_version


These values can be obtained by parsing td_user_agent with the Hive or Presto function [TD_PARSE_USER_AGENT](https://api-docs.treasuredata.com/en/tools/hive/td_hive_function_reference/#td_parse_user_agent).

The JS SDK version string will be added to the td_user_agent property for metric tracking and tracing. For example, JSSDK/4.0.1 will be added for the following browsers:

* Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7)
* AppleWebKit/537.36 (KHTML, like Gecko)
* Chrome/116.0.0.0
* Safari/537.36


## Limitations

Using Real-time segmentation requires routing enablement from the back end. Contact Treasure Data Support for assistance in enabling JS SDK 4.x for real-time processing. Be prepared to provide the following information to TD Support:

* Account number
* Database name
* Table name


Treasure Data anticipates removing this limitation in a future release.

For instructions on migrating to version 4.x see [Migrating to TD JS SDK 4.0](/products/customer-data-platform/integration-hub/streaming/td-javascript-sdk/migrating-to-td-js-sdk-4-0).