You are passing queryparams in your request, so to get those data, you need to write

var username = req.query.user;
var password = req.query.pass;   

& not params

And set status of response before sending response from server side

res.status(200).send(recordset);

Hello I recently started learning node js. I have the code showing below and that I want is html button to call a client-side function that this function make a GET request in my server-site function and return the result.

Client-Site

function login(userIn,passIn){
  var xhr = new XMLHttpRequest();
    xhr.onreadystatechange = function () {
      if (xhr.readyState !== 4) return;
      if (xhr.status >= 200 && xhr.status < 300) {
        const obj = JSON.parse(xhr.responseText);
        console.log(obj);
      }     
      else 
        console.log('error', xhr);    
  }
  xhr.open('GET','/login?user='+userIn+'&pass='+passIn, false);
  xhr.send();
}

Server-Site (login.js)

var express = require('express');
var app = express();

app.get('/login', function (req, res) {
    var username = req.params.user;
    var password = req.params.pass;   
    var sql = require("mssql");

    // config for your database
    var config = {
        ... 
    };
    // connect to your database
    sql.connect(config, function (err) {    
        if (err) console.log(err);
            // create Request object
        var request = new sql.Request();               
        // query to the database and get the records
        request.query('select * from admins', function (err, recordset) {
           if (err) console.log(err)
           // send records as a response
           res.send(recordset);
           sql.close();
       });
   });
});

const webserver = app.listen(8080, function () {
    console.log("running...");
});

Directory

Project
  node_modules
  www
      .html
      client.js
  login.js (server site function)

I think that my error is in the url of the client function.