Make any ReadableStream emit "line" events

emitLines.js

/**
 * A quick little thingy that takes a Stream instance and makes
 * it emit 'line' events when a newline is encountered.
 *
 *   Usage:
 *   ‾‾‾‾‾
 *  emitLines(process.stdin)
 *  process.stdin.resume()
 *  process.stdin.setEncoding('utf8')
 *  process.stdin.on('line', function (line) {
 *    console.log(line event:', line)
 *  })
 *
 */

function emitLines (stream) {
  var backlog = ''
  stream.on('data', function (data) {
    backlog += data
    var n = backlog.indexOf('\n')
    // got a \n? emit one or more 'line' events
    while (~n) {
      stream.emit('line', backlog.substring(0, n))
      backlog = backlog.substring(n + 1)
      n = backlog.indexOf('\n')
    }
  })
  stream.on('end', function () {
    if (backlog) {
      stream.emit('line', backlog)
    }
  })
}
module.exports = emitLines

test.js

var assert = require('assert')
  , emitLines = require('./emitLines')
  , Stream = require('stream')
  , stream
  , count

// 1
count = 0
stream = new Stream
stream.on('line', function (line) {
  count++
  assert.equal('test', line)
})
emitLines(stream)
assert.equal(0, count)
stream.emit('data', Buffer('test\n'))
assert.equal(1, count)