How to pass a function as callback?

Question

I have this JS code:

Download.prototype.insert = function(stocks, exchange, cb){
    var self  = this
      , count = stocks.length      

    stocks.forEach(function(stock){     
        save(stock, done)
    })

    function save(stock, cb){
        self.mysql.query("my query", [exchange.id, stock.Symbol], function(err, rows){
            if (rows && rows.length > 0) 
                self.mysql.query("my query", [rows[0].id, stock.DateTime, stock.Close], cb)
            else cb()   
        })      
    }

    function done(){                
        count--
        if (count === 0) return cb()        
    }
}

as you can see I pass a callback to the save() function, I would like to know if i can separate the queries to avoid using of function(err, rows){ .... }

the problem is that function wait two parameters err and rows , so How can I also pass a custom third parameter (the cb() function) ?

Thanks

Answer 1

I hope I understood your question right ^^

To wrap your callback parameter, you can create a function that returns an anonymous function (the actual callback). The cb parameter gets wrapped into the context of the anonymous function:

function queryDetails(cb){
  return (
    function(err, rows){
      if(rows && rows.length < 0){
        //mysql.query ...
      }else{
        cb()
      }
    })
 };
 mysql.query("query", ...., queryDetails(doneCallback));

Have fun!