Pausing readline in Node.js

Question

Consider the code below ... I am trying to pause the stream after reading the first 5 lines:

var fs          = require(\'fs\');
var readline    = require(\'r         


        

Answer 1

Somewhat unintuitively, the pause methods does not stop queued up line events:

Calling rl.pause() does not immediately pause other events (including 'line') from being emitted by the readline.Interface instance.

There is however a 3rd-party module named line-by-line where pause does pause the line events until it is resumed.

var LineByLineReader = require('line-by-line'),
    lr = new LineByLineReader('big_file.txt');

lr.on('error', function (err) {
  // 'err' contains error object
});

lr.on('line', function (line) {
  // pause emitting of lines...
  lr.pause();

  // ...do your asynchronous line processing..
  setTimeout(function () {

      // ...and continue emitting lines.
      lr.resume();
  }, 100);
});

lr.on('end', function () {
  // All lines are read, file is closed now.
});

(I have no affiliation with the module, just found it useful for dealing with this issue.)