Node.js: Count the number of lines in a file

Question

I have large text files, which range between 30MB and 10GB. How can I count the number of lines in a file using Node.js?

I hav

Answer 1

since iojs 1.5.0 there is Buffer#indexOf() method, using it to compare to Andrey Sidorov' answer:

ubuntu@server:~$ wc logs
  7342500  27548750 427155000 logs
ubuntu@server:~$ time wc -l logs 
7342500 logs

real    0m0.180s
user    0m0.088s
sys 0m0.084s
ubuntu@server:~$ nvm use node
Now using node v0.12.1
ubuntu@server:~$ time node countlines.js logs 
7342500

real    0m2.559s
user    0m2.200s
sys 0m0.340s
ubuntu@server:~$ nvm use iojs
Now using node iojs-v1.6.2
ubuntu@server:~$ time iojs countlines2.js logs 
7342500

real    0m1.363s
user    0m0.920s
sys 0m0.424s
ubuntu@server:~$ cat countlines.js 
var i;
var count = 0;
require('fs').createReadStream(process.argv[2])
  .on('data', function(chunk) {
    for (i=0; i < chunk.length; ++i)
      if (chunk[i] == 10) count++;
  })
  .on('end', function() {
    console.log(count);
  });
ubuntu@server:~$ cat countlines2.js 
var i;
var count = 0;
require('fs').createReadStream(process.argv[2])
  .on('data', function(chunk) {
    var index = -1;
    while((index = chunk.indexOf(10, index + 1)) > -1) count++
  })
  .on('end', function() {
    console.log(count);
  });
ubuntu@server:~$