Anonymous functions syntax in CoffeeScript

Question

I've been looking at CoffeeScript and I'm not understanding how you would write code like this. How does it handle nested anonymous functions in its syntax?

;(function($) {
          var app = $.sammy(function() {

            this.get('#/', function() {
              $('#main').text('');
            });

            this.get('#/test', function() {
              $('#main').text('Hello World');
            });

          });

          $(function() {
            app.run()
          });
        })(jQuery);

The CoffeeScript website has a Try CoffeeScript feature, which compiles to JavaScript on the fly. I was able to figure out the answer in a few minutes playing around with it. — Joey Adams
– Joey Adams, Commented Nov 12, 2010 at 16:13

Matt Briggs · Accepted Answer · 2010-11-12 16:03:48Z

44

didn't actually compile it, but this should work

(($) ->
  app = $.sammy ->

    this.get '#/', ->
      $('#main').text '' 

    this.get '#/test', ->
      $('#main').text 'Hello World'

  $(->
    app.run()
  )
)(jQuery);

answered Nov 12, 2010 at 16:03

Matt Briggs

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1 Comment

Derek Dahmer Over a year ago

Since coffeescript automatically wraps code in an anonymous function anyway, you can actually just put $ = jQuery at the top of your file and take out the calling of an anonymous function with jQuery as a parameter.

Trevor Burnham · Accepted Answer · 2011-03-06 02:54:45Z

36

Matt's answer is correct, but here's an alternative method:

In CoffeeScript 1.0 (released a few weeks after this question was posed), a do operator was introduced that runs the function that immediately follows it. It's mostly used for capturing variables in loops, since

for x in arr
  do (x) ->
    setTimeout (-> console.log x), 50

(which passes a reference to x into the anonymous function) behaves differently than

for x in arr
  setTimeout (-> console.log x), 50

The latter will simply output the last entry in arr repeatedly, since there's only one x.

Anyway, you should be aware of do as a way of running an anonymous function without the extra parentheses, though its capabilities with respect to argument-passing are a bit limited at the moment. I've raised a proposal to broaden them.

Currently, the equivalent of your code example would be

do ->
  $ = jQuery
  ...

If my proposal is accepted, it will be possible to write

do ($ = jQuery) ->
  ...

instead.

answered Mar 6, 2011 at 2:54

Trevor Burnham

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1 Comment

user133408 Over a year ago

This method is really nice, as accounting for coffeescript philosofy it does not require any closing brackets

lexich · Accepted Answer · 2013-02-06 11:21:01Z

5

Short variant

do ($=jQuery)->
 app = $.sammy ->
   @get '#/', -> $("#main").text ''
   @get '#/test', -> $('#main').text 'Hello world'
 $ -> app.run()

answered Feb 6, 2013 at 11:21

lexich

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