javascript - How to check if row exists in mysql, in Node js -

i check in record exists in mysql, working in node js. code is:

//some code before classes  (var m = 0; m <= (classes.length-1); m++) {     var myurl = classes[m];      (function(myurl){         var connection = mysql.createconnection({             host: 'localhost',             user: 'root',             password: 'password',             database: 'mydatabase',         });         connection.connect();          //how write query correctly?         var query = connection.query('select * mydatabase urllink=? limit 1', [myurl], function(err, rows, fields) {             if (err)                  throw err;              sqlnames = rows;             lognames();              //if urllink not present in mydatabase, want proceed with:             request(myurl,  function(err, resp, body) {                 // ...             }         });          function lognames() {             console.log(sqlnames);         }          connection.end();     }; })(myurl); 

so, want check if record exists in database, , if not exist want process request, , add database. error:

connection not defined

the reason connection undefined because creating in javascript closure. when initialize variable inside function, scope prevents being accessed outside function.

here sample code:

var myurl = classes[m]; var connection = mysql.createconnection({ // notice how not in function?   host     : 'localhost',   user     : 'root',   password : 'password',   database : 'mydatabase', }); connection.connect(); // before. 

without knowing database schema, cannot tell if proper query, looks correct doing.