socket.io callbacks

Question

socket.io callbacks

I have the following code:

  client.keys("key_"+id, function (err, replies){
      if (replies.length > 0){
        client.sunion(replies,function (err, replies){
          {...}
        });
      }else{...}
     });

below I have this function

pg.connect(conString, function(err, client) {some code});

But I want execute pg.connect instead of ... in first piece of code. How best to do to avoid copying code and memory leaks, pg.connect function will be the same in all {...}.

With copying code this will be look like:

    client.keys("key_"+id, function (err, replies){
      if (replies.length > 0){
        client.sunion(replies,function (err, replies){
          pg.connect(conString, function(err, client) {some code});
        });
      }else{pg.connect(conString, function(err, client) {some code});}
     });

javascript
node.js
callback

Answer 1

Remember that you are working with JavaScript and can define little helper functions to reduce your typing...

function withConnect( callback ) {
    return pg.connect( conString, callback );
}

for instance will save you some time... But what if the error handler is always the same?

function withConnect( callback ) {
    return pg.connect( conString, function( err, client ) {
        if ( err ) {
           handleError( err );
        }
        // we might still want something special on errors...
        callback.apply( this, arguments );
    }
 }

You could even abstract simple insert/update style queries this way.

Answer 2

You can try (if the "some code" sections are the same):

function connectFunc() {
    return function (err){
       pg.connect(conString, function(err, client) {some code});
    };
}

client.keys("key_"+id, function (err, replies){
    if (replies.length > 0){
        client.sunion(replies, connectFunc());
    } else { connectFunc()(err)}
});

Or, if the "some code" varies:

function connectFunc(some_code) {
    return function (err){
       pg.connect(conString, function(err, client) {some_code();});
    };
}

client.keys("key_"+id, function (err, replies){
    if (replies.length > 0){
        client.sunion(replies, connectFunc(function(){some code}));
    } else { connectFunc(function(){some other code})(err)}
});