Quick Node script to merge to extend one JSON file with another and save it

extend-and-save.js

/*global require console */

var _ = require('underscore'),
    fs = require('fs'),
    data = JSON.parse(fs.readFileSync('./data.json', 'utf-8')).data;

_.each(data, function(item) {

  var newJson = item[0],
      files = item[1];

  _.each(files, function(file) {
    var path = '.' + file,
        oldJson = JSON.parse(fs.readFileSync(path, 'utf-8')),
        newJson = _.extend(oldJson, newJson),
        printableJson = JSON.stringify(newJson, null, 2);

    fs.writeFile(path, printableJson, function(err) {
      if (err) throw('File save error: '+ err);
      console.log('file saved');
    });

  });

});

What about big json files (which exceed the limit of 512/1024 mb)?