Underscore js object difference

underscorejs.object.diff.js

var Objcontains = function(oldO, newO) {
        var changed = {};
        _.each(newO, function(v, i) {
            if (oldO[i] != undefined) {
                if (Array.isArray(v)) {
                    changed[i] = _.difference(v, oldO[i]);
                } else if (typeof v == 'object') {
                    changed[i] = Objcontains(oldO[i], v);
                } else {
                    if (oldO != undefined && (oldO[i] == undefined || oldO[i] != v)) {
                        changed[i] = v;
                    }
                }
            } else {
                changed[i] = v;
            }
        });
        return changed;
    }