Agreed. I spent the last few months building my first Node.js app (and MongoDB) ...

nailer · on Feb 28, 2011

> 2. Coding async is weird at first, but you may grow to love it (as I have). Over the months, I've discovered many cool tricks and patterns that help keep the nesting to a minimum.

Can you share a few? Either here or as a blog post?

mjs · on Feb 28, 2011

If you have a function foo() that takes a callback as an argument i.e. something like:

  foo(..., function (n) {
     // closure over q, r, s
  });

Then what you can do is create a separate function, bar() that takes q, r, s as an argument, and returns a function:

  function bar(q, r, s) {
    return function(n) {
      // still has dependency on q, r, s
    }
  }

Once you have bar(), the foo() call above can be written as:

  foo(..., bar(q, r, s));

and you save one level of nesting. (This also makes the dependencies explicit, which is helpful.)

The main loop of

https://github.com/ithinkihaveacat/node-fishback/blob/ce5f9c...

does quite a lot of this, if you want a real example.

jlyke · on Feb 28, 2011

This technique reminds me of Lambda Lifting: http://en.wikipedia.org/wiki/Lambda_lifting

svetlyak40wt · on Feb 28, 2011

Why not to write it in a much simplier way? Like this:

  function bar(n) {
    // still has dependency on q, r, s
  }
  foo(..., bar);

mjs · on Feb 28, 2011

Yeah, that's nicer if bar() can be defined at the same "level" as foo() but if it makes more sense to move it somewhere else the closed-over variables need to be passed.

htsh · on Feb 28, 2011

We've been using the flow control helpers in async.js to help us with the nesting issue: (https://github.com/caolan/async).

We use the waterfall most, as it allows one to run an array of function in a series with a callback at the end of the series.