sql.js

function NumRegUnico( obj, transaction ) { 
  
    console.log("Entering NumRegUnico");
    
    return new Promise( ( resolve, reject ) => {
        sql.connect( config ).then( recordsets => {
            var request = new sql.Request( transaction );

            request.output( 'NuevoNumReg', sql.char );
            request.execute( 'dbo.uspNuevoRegistro' ).then( recordsets => {
                console.log( "output param: " + request.parameters.NuevoNumReg.value ); // new inc'd numreg
                obj.numreg = request.parameters.NuevoNumReg.value; 
                resolve( obj );
            });
         });
    });
}