Avoiding local variables

Question

I often encounter problems in terms of design if it comes to this point:

var pages,
    book
;

Book.findOne( { title: "First Book" }, function(err, doc) {
  pages = doc.pages;

  console.log( pages );
} );

res.json(pages, 200);

pages is undefined, though I set it to doc.pages. If I move the res.json(pages, 200) into the callback of findOne this script works perfectly.

Am I following a wrong pattern/code design when it comes to JavaScript or is there a solution to keep the res.json() out of the callback, apart from making pages global?

davidchambers · Accepted Answer · 2012-01-22 22:27:57Z

6

The problem is that you're passing Book.findOne a callback to be executed when a match is found. Afterwards you're invoking res.json, and passing it pages as an argument. It's important to understand that the callback will not have been executed by this time. Are you able to move the response inside the callback function?

Book.findOne({title: 'First Book'}, function (err, doc) {
  res.json(doc.pages, 200)
})

edited Jan 22, 2012 at 22:27

answered Jan 22, 2012 at 22:21

davidchambers

25.1k18 gold badges81 silver badges110 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Julius F Over a year ago

Yes, that's perfectly fine. I already assumed that this is the more common usage patten in Javascript to work via Callbacks since code is executed asynchroniosly and not strictly from one line to the other.

fent Over a year ago

@daemonfire300 code is not executed asynchronously. Callbacks are called asynchronously.

Collectives™ on Stack Overflow

Avoiding local variables

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related