Coffeescript/Javascript variable scope

问题:

I'm not really sure why i do not have access to the @date (this.date) variable from the context of the anonymous function defined in C.f()

class C
  constructor: () ->
    @date = new Date()

  f: () ->
    $(document).keydown( (e) ->
      alert(@date)
    )

Could someone comment on that?

回答1:

This is happening because inside the keydown event handler, the this value will not refer to your object, it will refer to the DOM element.

For that purpose, you can use => (the fat arrow), that will bind the handler's this value to the parent this:

class C
  constructor: () ->
    @date = new Date()

  f: () ->
    $(document).keydown( (e) =>
      alert(@date)
    )