Tiny linereader implementation (CoffeeScript)

Data processing in nodejs requires handling data in Buffer objects.
Here is a quick implementation for parsing + appending incoming buffer data to an array.

  readline = (trg) ->
    len0 = trg.length
    (buf) ->
      len    = trg.length
      lines  = "#{buf}".split "\n"
      if len - len0 > 0 then trg[len - 1] = trg[len - 1] + lines[0]
      else                   trg.push lines[0]
      trg.push line for line in lines[1..]
      return

  selfTest = do ->
    input = []
    buf = (str) -> input.push new Buffer str
    buf "abc\nx"
    buf "yz\n"
    buf "12"
    buf "34"
    buf "\n"

    output = ["opq",""]
    input.forEach readline(output)

    assert.equal output.join(";"), "opq;;abc;xyz;1234;", "Messed up!"