If you want to test your script live, the IoT Gateway comes with a script sandbox called the Calculator. It's available from the mail menu. In it, you can type any script you like, and see the results as you press ENTER.
For a complete script reference, see the local resource /Script.md hosted by your IoT Gateway. You can also access it here: https://waher.se/Script.md.
Before deploying a solution based on the IoT Gateway, you should either protect the sandbox by requiring users to log in before they can access the sandbox, or you should remove it completely by removing the page and the web service Waher.WebService.Script.
Script sandbox