Question

In CoffeeScript, this:

class Foo
  method: (x) ->
    x+1

Compiles to:

// Generated By CoffeeScript
Foo = (function() {
  function Foo() {}
  Foo.prototype.method = function(x) {
    return x+1;
  }
  return Foo;
})()

Which seems a bit excessive. The following should be functionally identical:

// Generated by Dave
function Foo() {}
Foo.prototype.method = function(x) {
    return x+1;
}

What is the motivation for the extra “closure” wrapper?

This is not merely an idle question of styling; it has implication to overall code size.

The Coffee version minifies into 84 bytes:

Foo=function(){function e(){}return e.prototype.method=function(e){return e+1},e}();

My version minifies into only 61 bytes:

function Foo(){}Foo.prototype.method=function(e){return e+1};

23 bytes is silly kinds of irrelevant, but in a project with many many classes, overhead begins to add up.

Ok, I wrote an answer below refuting the byte size theory … for any reasonable class, the Coffee method is going to be smaller.

There’s probably other reasons too. Help me think of them.

Answer 1

Jeremy answers this over in a related question – it looks like the primary intent is to avoid triggering an IE bug.