It seems like the pattern that you are interested in is something like this:
//file 1
var xy = (function (that) {
that.prop1 = 1;
return that;
}(xy || {}));
//file2
var xy = (function (that) {
that.prop2 = 2;
return that;
}(xy || {}));
This will result in a single global object xy
that has two properties:
xy = {
prop1: 1,
prop2: 2
};