Type Casting in Apps Script
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First time on StackOverFlow! 

I am working on building an app that takes in a value through a UI Form TextBox. Once that form is submitted it calls a method that then appends a "/" to the value. The problem is that .append() is not available, because getElementById() returns a GenericWidget object and thus cannot be operated on as if it were a string. I have tried type casting it use .toString() in the var userinput = app.getElementById('input').toString; call and afterward using userinput = userinput.toString. 

I have been working with Apps Script for about a month and a few days now and I think that casting to a different type other than GenericWidget would be helpful for anyone who wants to modify a value in a type specific way after passing the value to another method. 

I have also done a good bit of research trying to find a solutiong for my problem but like a couple times in the past working with Apps Script I find that since it is a younger language there isn't as much helpful information as there is with languages like Javascript, HTML, and XML. Any help is appreciated.