@yourfriendkarol Yes, a Javascript source code file. You can put all settings you need into a nice JS object, say "config":
var config = {
// Setting 1
"setting1": "value1"
// Setting 2
,"setting2": "value2"
//...
// Setting N
,"settingN": "valueN"
};
It can be of any structure you require.
The source file also can define other commonly used variables and functions.
XML... I don't think you need to bother with that.