Beware: Coffeescript "in" is not the Javascript "in"

The Javascript in operator does what Hash#has_key? does in Ruby: Return whether an object has a property.
However, Coffeescript has its own in operator that checks for array inclusion. To check whether an object has a property, use of:

Javascript

Copy'name' in {name: 'Horst'} # => true

Coffeescript

Copy# wrong
'name' in {name: 'Horst'} # => false

# correct
'name' of {name: 'Horst'} # => true
1 in [1,2,3] # => true

True story.