CoffeeScript, When to use fat arrow (=>) over arrow (->) and vice versa

Question

When building a class in CoffeeScript, should all the instance method be defined using the => (\"fat arrow\") operator and all the static methods being defin

Answer 1

Usually, -> is fine.

class Foo
  @static:  -> this
  instance: -> this

alert Foo.static() == Foo # true

obj = new Foo()
alert obj.instance() == obj # true

Note how the static method return the class object for this and the instance returns the instance object for this.

What's happening is that the invocation syntax is providing the value of this. In this code:

foo.bar()

foo will be the context of the bar() function by default. So it just sorta works how you want. You only need the fat arrow when you call these function in some other way that does not use the dot syntax for invocation.

# Pass in a function reference to be called later
# Then later, its called without the dot syntax, causing `this` to be lost
setTimeout foo.bar, 1000

# Breaking off a function reference will lose it's `this` too.
fn = foo.bar
fn()

In both of those cases, using a fat arrow to declare that function would allow those to work. But unless you are doing something odd, you usually don't need to.

So use -> until you really need => and never use => by default.