Help with pulling User Role info with Javascript

Goal/Background: I have a table that lists all the users of my application and I would like to be able to add each user's Role to their record.
I was able to pull the user role info via API_GetUserRole and parse that info with a simple javascript snippet that writes to the console. 
Question: How do I write the output of the javascript to the field or another field instead? Is there a way to do this automatically so when a new user is added the role is pulled?

I don't have much knowledge with javascript so any information is greatly appreciated. 

This is what I have so far in my URL formula field:

var Text ticket = "TicketHere";
var Text usrID = "userIDHere";
var Text apppToken = "appTokenHere";
var Text urlRole = URLRoot() & "db/" & "bpeu9wky6" & "?a=API_GetUserRole&ticket=" &$ticket& "&apptoken=" & $apppToken &"&inclgrps=1&userid="& $usrID ;

"javascript: " & 
  "$.get('" & $urlRole & "',function(data,success) {" & 
        "console.log(data);" &
        "var user = data.getElementsByTagName('role')[0].getElementsByTagName('name')[0].innerHTML;" & 
        "console.log(user);" & 
  "});"​

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Best,
Austin
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