This sample script is for retrieving a key with the maximum value from an object. This can be also used by Google Apps Script.
var obj = {"a": 5, "b": 4, "c": 3, "d": 2, "e": 1};
var res = Object.keys(obj).reduce(function(a, c) {
return obj[a] > obj[c] ? a : c;
});
Logger.log(res); // >>> a