Question

So say I’ve got a function:

function grabOldestJob() {
  var client = mysql.createClient({
    user: dbConfig['USER'],
    password: dbConfig['PASS'],
  });

  client.query('USE '+dbConfig['DATABASE']);

  client.query('SELECT url FROM '+dbConfig['JOB_TABLE']+' ORDER BY added ASC LIMIT 1 ',
    function selectCb(err, results, fields, passed) {
      if (err) {
        throw err;
      }
      client.end();
      fetchFeed(results[0]['url']);
    }
  );
}

What I need is the results[0][‘url’] buried in the inline function, so either I’d like to get that variable out of that function so I can use it to return the grabOldestJob function or pass another function into the inline function so I can use results[0][‘url’] as a parameter.

I’m very new to the concepts of node.js and would like to make my code as ‘proper’ as possible. This function is the first in a process, it pulls a url out of a database, passes that to get fetched from the remote server, the xml feed gets parsed and certain bits get stored in a database. I’m hoping using the ability of node to ‘run lots of things at once’ I’ll be able to fetch->parse->save many feeds at the same time. Any best practice tips for this would also be greatly appreciated.

Answer 1

Use callback functions for this.

Like the client.query(query,callback) function does. You pass in the data and a callback function that gets called if the processing completed. Do the same with your fetchFeed(url,callback) function.

...
client.end();
fetchFeed(results[0]['url'],function(result){
    // here 'result' contains the fetched feed and can be stored into the database
});
...

---

function fetchFeed(url,cb){
    // download feed here and call cb(downloaded_data) when finished, passing the downloaded data to the cb() function
}

Have a look at: Understanding the node.js event loop