express rest api with pagination

// From https://codeforgeek.com/2017/12/server-side-pagination-using-node-and-mongo/


router.get('/users',(req,res) => {
  var pageNo = parseInt(req.query.pageNo)
  var size = parseInt(req.query.size)
  var query = {}
  if(pageNo < 0 || pageNo === 0) {
        response = {"error" : true,"message" : "invalid page number, should start with 1"};
        return res.json(response)
  }
  query.skip = size * (pageNo - 1)
  query.limit = size
  // Find some documents
       mongoOp.count({},function(err,totalCount) {
             if(err) {
               response = {"error" : true,"message" : "Error fetching data"}
             }
         mongoOp.find({},{},query,function(err,data) {
              // Mongo command to fetch all data from collection.
            if(err) {
                response = {"error" : true,"message" : "Error fetching data"};
            } else {
                var totalPages = Math.ceil(totalCount / size)
                response = {"error" : false,"message" : data,"pages": totalPages};
            }
            res.json(response);
         });
       })


       
     exp: http://localhost:3000/api/users?pageNo=1&size=10