Need help understanding class member meanings about coffeescript

[Inve1951]

class Test
  @foo = "foo" # static member (shorthand for `Test.foo = "foo"`)
  bar = "bar" # class-scoped variable (behaves like a private static)
  baz: "baz" # instance member

With : in a class body you assign a prototype property. This is only done once.
Unless the value is a primitive, all class instances inherit the same object reference, which causes the behavior you see.

Default values for non-primitives should be assigned in the constructor (@member = value).