Need to know which transaction is matched in the VSI without going to the DevTest Portal.
All supported DevTest releases.
Transaction Id can be found in DevTest Portal-->Inspection View and the knowledge article Find matching transaction id details in DevTest Portal will provide more information.
The above code will create a property transactionId which has the matched Transaction Id from VSI.
Instead of the Execute Script step, Scripted Assertion can also be created in VS Image Response Selection step with the above code but make sure the assertion is executed to capture the matched Transaction Id.
Look at the documentation on Execute Script Step and Scripted Assertion for more information in DevTest Techdocs.