@campaignerforlife,
Some functions are not available or not compatible with the specific version of JavaScript used in Adobe Campaign.
Regarding the String.startsWith() function, it is part of ECMAScript 6 (ES6) and may not be available in some older versions of JavaScript.
To check your version of JavaScript, you can run the following code: console.log("JavaScript version:", typeof Symbol());-
If the output is "function", then you are using ES6 or a later version of JavaScript. If the output is "undefined", then you are using an older version of JavaScript.
Make sure that you are calling the function on a string object, and not just as a standalone function.
For example, you should call "hello world".startsWith("hello"), not just startsWith("hello").
Specifically, the JavaScript API documentation provides information on the available functions and how to use them.