How to parse the data from "rows" object in node.js,express.js,mysql2

Try this (this is really basic):

   connection.query('SELECT * from pass', function(err, rows) {
     res.json(rows);

     var user = rows[0].userid;
     var password= rows[0].password;

   });

 connection.query('SELECT * from pass', function(err, rows) {
      data = rows[0];
     let user = data.userid;
     let password= data.password;
     res.json(rows);

   });

[{"userid": "test","password": "test"}]

This is an Array of Objects. So: First loop over the array to get a single object and then extract its properties:

for (var i = 0; i < rows.length; i++) {
    var row = rows[i];
    console.log(row.userid);
}