module csv with global variables, coffeescript and callbacks

I'm using node-csv-parser by wdavidw with coffeescript. I know (or should know) about variables scope, bind, globals, but looking at this code snippet I couldn't understood what do @array varable lose its values or even be assigned.

script.coffee:

    require 'csv'
    find_lines = ->
        @array = []
        csv()
            .fromPath("#{__dirname}/Cities.csv", {delimiter:";"})
            .on 'data', (data, index) =>
                @array = data

    console.log @array

    find_lines()

Running the script.coffe:

➜ modules git:(master) ✗ coffee script.coffee

The code output is:

quoted false
quoted false
quoted false
quoted false

When it should be (according to csv values):

City 1
City 2
City 3

Using the .transform method from csv parser produces the same error.

Did I misunderstand how node-csv-parser works or any problem with this module?

Thanks in advance!

Let's start with one possible implementation:

csv = require 'csv'

find_lines = ->
  array = []
  csv()
  .fromPath("#{__dirname}/Cities.csv", {delimiter:";"})
  .on 'data', (data) ->
    array.push data[0]
  .on 'end', ->
    console.log array

find_lines()

Note that you probably want something other than array.push data[0] in the 'data' callback.

You don't need to use @array here because the array variable is available to the 'data' and 'end' callbacks. This also eliminates the need for the fat arrow function bindings. In this implementation, the array variable is only visible in the scope of find_lines so you won't be able to log its contents from outside the function call.

Alternatively, you can make array visible outside of find_lines by moving it to the module scope like so:

csv = require 'csv'
array = []

find_lines = ->
  csv()
  ...

However, (and this is the really critical point), the array variable will not be modified until after the rest of your module code (including any calls to console.log outside of find_lines) has already executed. If this is unclear, you should brush up on the fundamentals of callbacks and execution order in node.js.

Other minor issues

  1. require 'csv' should be csv = require 'csv'
  2. array was not being modified with data, it was being overwritten on each new csv row