Cannot find module 'mssql' nodejs

Nowdays (2021) you have to read this manual.

And basically you have to install Microsoft SQL Server client for Node.js like

npm install mssql

You can test it by following code.

test-mssql-server.js

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

app.get('*', (req, res) =>  {
  
    var sql = require("mssql");

    // config for your database
    var config = {
        user: 'sa',
        password: 'mypssssss1!',
        server: 'MyComputerName001\\SQL2016Instance', 
        database: 'MyDbName' 
    };

    (async function () {
        try {
            let pool = await sql.connect(config)

            let result1 = await pool.request()                
                .query('select * from Devices')
   
            // console.dir(result1) 
            // send records as a response
            res.send(result1);
        } catch (err) {
            //  error checks
        }
    })();
    
    sql.on('error', err => {
        // error handler
        console.log(err);
    });

    
});

//start listening
var port = process.env.PORT || 5321;
app.listen(port, function () {
    console.log('Application started on ' + new Date());
    console.log("Listening on " + port);
});

After this start your node.js app in command prompt

node test-mssql-server.js

Now open your browser and go to http://localhost:5321/

This is because you don't have the node module installed in your system. Install this using
npm install mssql