var fst = require('fs-tail-stream');
var fs = require('fs');
var ws = fs.createWriteStream(tmpFile, { flags: 'a' });

// file with the text 'hello' in it
var tmpFile = '/tmp/my-temp-file.txt';

// same parameters as `fs.createReadStream`, but pass through `tail: true`
fst.createReadStream(tmpFile, { encoding: 'utf8', start: 80, tail: true })
  .on('sync', function () {
    // called when at the end of the file
    var self = this;
    // write some new data to the file
    ws.write('world', 'utf8', function (err) {
      // stop watching for files, and let the file stream end
      // otherwise the file watching will be indefinite and the process
      // won't' exit
      self.close();
    });
  })
  // will print out both the existing contents of the file, plus the
  // newly added data
  .on('data', console.log);
  // prints out:
  //   hello
  //   world