read from a text file and remove all duplicated rows

rename.js

var fs = require('fs');

function readLines(input, func) {
  var remaining = '';

  input.on('data', function(data) {
    remaining += data;
    var index = remaining.indexOf('\n');
    while (index > -1) {
      var line = remaining.substring(0, index);
      remaining = remaining.substring(index + 1);
      func(line);
      index = remaining.indexOf('\n');
    }
  });

  input.on('end', function() {
    if (remaining.length > 0) {
      func(remaining);
    }

    var keys = Object.keys(mailList);
    for (var index in keys) {
      console.log(keys[index]);
    }
  });
}

var mailList = {};

function func(data) {
  var key = data.toLowerCase().trim();
  if (!mailList.hasOwnProperty(key)) {
    mailList[key] = 1;
  }
}

var input = fs.createReadStream('input.txt');
readLines(input, func);