Question

I was using js2coffee but it doesn’t seem to translate because I get an unexpected identifier.

$.fn.wait = function( ms, callback ) {
    return this.each(function() {
        window.setTimeout((function( self ) {
            return function() {
                callback.call( self );
            }
        }( this )), ms );
    });
};

My coffee version:

$.fn.wait = (ms, callback) ->
  @each ->
    window.setTimeout ((self) ->
      ->
        callback.call self
    (this)), ms

Answer 1

First clean up your JavaScript version so that it isn’t trying to be overly clever and difficult to read; the inlined self-executing function really doesn’t do anything for you except make the people maintaining and reading your code hate you:

$.fn.wait = function( ms, callback ) {
    return this.each(function() {
        var _this = this;
        window.setTimeout(function() {
            callback.call(_this);
        }, ms);
    });
};

That’s less noisy and easier to grok at a glance. The var _this = this trick is generally replaced by a fat-arrow (=>) in CoffeeScript so we’re left with this:

$.fn.wait = (ms, callback) ->
    @each(->
        fn = () => callback.call(@)
        setTimeout(fn, ms)
    )

Yes, parentheses are often optional in CoffeeScript but optional and forbidden are different words so I tend to include the parentheses to make the structure easier to see. You could also skip the fn variable with something horrific like this:

setTimeout(
    => callback.call(@)
, ms)

or this:

setTimeout (=> callback.call(@)), ms

but throwing an extra variable into the mix is, IMO, much easier on the eyes.

Demos:

• CoffeeScript: http://jsfiddle.net/ambiguous/y44Fp/
• JavaScript: http://jsfiddle.net/ambiguous/TVkMh/