Question

Kept on seeing this pattern in code, but couldn’t find any reference to it in google or SO, strange. Can someone point me to reference for this.async() function?

  var done = this.async();
  // ...
  $.get(path, function(contents) { // or some other function with callback
    // ...
    done(JST[path] = tmpl);
  })

Answer 1

It is a way to work around the problem of this escaping inside callback. Without this extra reference the code would look like this:

$.get(path, function(contents) { // or some other function with callback
  //Wrong! `this` might no longer point to your object
  this.done(JST[path] = tmpl);
})

Unfortunately! this inside response callback is not the same as this outside of it. In fact it can be anything, depending on what $.get (calling the callback using) decides it to be. Most of the people use extra reference named that for the same purpose:

var that = this;
// ...
$.get(path, function(contents) { // or some other function with callback
  // ...
  that.async(JST[path] = tmpl);
})

This pattern also seems reasonable and readable.

Oh, and if you are curious about this syntax:

done(JST[path] = tmpl)

This is an assignment used as an expression. The value of assignment is the right-hand side, so this code is equivalent to:

JST[path] = tmpl;
done(tmpl);