db.system.js.save({"_id":"some_function_name",
    value: function(acc, limitTime) {
        allAcc = {};
        distinct1 = [];
        distinct2 = [];
        distinct1Map = [];
        distinct2Map = [];
        db.coll1.find({fromId:{$in : acc}, p:{$in : acc}, so:{$gte : limitTime} }, {_id:0, toId:1, so:1}).sort({so : -1}).forEach(function(mess) {
                // some if-else operation
        });
        allAcc["u"] = distinct1Map;
        db.coll2.find({ so:{$gte : limitTime}, fromId:{$in : acc}}, {_id:0, toId:1, so:1}).sort({so : -1}).forEach(function(group_mess) {
                // some if-else operation
        });
        allAcc["g"] = distinct2Map;
        return allAcc;
    }}