Question

Given the following coffeescript code:

class Animal
  constructor: (@name) ->
  speak: (things) -> "My name is #{@name} and I like #{things}"

This is generated:

var Animal = (function() {
  function Animal(name) {
    this.name = name;
  }
  Animal.prototype.speak = function(things) {
    return "My name is " + this.name + " and I like " + things;
  };
  return Animal;
})();

But why isn’t this more idiomatic code generated?

var Animal = function Animal(name) {
  this.name = name;
};
Animal.prototype.speak = function(things) {
  return "My name is " + this.name + " and I like " + things;
};

I know that coffeescript wraps a lot of stuff in anonymous functions to control scope leak, but what could leak here?

Answer 1

The generated code makes it possible to reliably have named functions in Internet Explorer. (In this case, “Animal”.) If you simply use a named function at top-level scope, it will conflict with any var Animal = declarations that might be present … even in lower scopes, preventing them from being referenced correctly. To work around the IE bug, we include the function wrapper around the class definition.