If you want to call the parent method and then decorate the result with more information before it's returned, you can do it like this with pure CoffeeScript:
class Parent
defaults: () ->
return {
tension: 0.8
}
class Sub extends Parent
defaults: () ->
r = super
r.fill = true
return r
sub = new Sub
sub.tension # 0.8
sub.fill # true
Using a library like http://underscorejs.org/ would probably make it a little prettier as you could do:
defaults: () ->
_.extend super, {
fill: true
}