javascript - How do I switch connections using Node JS and mssql -

i have situation need query multiple sql servers bunch of data. so, iterating on sql servers first , iterating on queries have run. in caller function, have below code

config.servers.foreach((element) => {     sqlserver = element.server;     element.queries.foreach(function(configquery) {         jsonkey = configquery.key;         sqlquery = configquery.query         sqldatabase = configquery.database;         var out;         if (configquery.parameter) {             sqlquery = sqlquery + " " + configquery.parameter + " = '" + partnumber + "'";         }         sqlhelper.sqlfun(sqlquery, sqlserver, sqldatabase, jsonkey, callback)     }) 

and sqlfun referes below function

let connection ; function poolit (sqlquery,sqlserver,databasename) {  if(!connection) {  //sqlserver_temp = sqlserver  //instead of checking if connection defined  //we have check if connection open   var dbconfiguration = {   driver: 'msnodesqlv8',   server: sqlserver,   database: databasename,   options: {       trustedconnection: true   } }  connection = sql.connect(dbconfiguration);   } }  function runquery(sqlquery,sqlserver,databasename,sqlkey, callback) {   poolit(sqlquery,sqlserver,databasename)   connection.then(pool =>{   return pool.request().query(sqlquery)   }).then(result=>{   if(callback)   return callback(null,result.recordset, sqlkey )    }).catch(err=>{   if(callback)   {     console.log(err)     return callback(err,null, sqlkey)    }    })  } module.exports.sqlfun = runquery; 

the problem facing is, sql server connections trying establish, of connecting same sql server. understand has due function poolit checking there if connection exists or not , if exists, coming out of loop. i'd understand how close connection once done executing queries in iteration first sql server? tried sql.close() , connection.close() not working. program hangs long time if use them.