Streams

Do_something_before_all_loaded

var fs = require('fs');
var stream = fs.createReadStream('./test.mp4');

stream.on('data', function(data) {
  console.log('loaded part of the file');
});

load_after_whole_file

var require('fs');
fs.readFile('./test.json', function(err, err){
  if (err) {
    return console.log(err);
  }

  console.log('test file is loaded:\n', data);
});

write_part_of_file_before_whole_is_loaded

var fs = require('fs');
var request = require('request');

var stream = request('http://i.imgur.com/dmetFjf.jpg');
var writeStream = fs.createWriteStream('test.jpg')

stream.on('data', function(data) {
  writeStream.write(data)
});