NodeJS Process File then Output to File

gistfile1.js

var fs = require('fs');
fs.readFile('cats.txt', function(err, data) {
    if(err) throw err;
    var array = data.toString().split("\n");

		var lookup = array.map(function(line) {

			var significant = line.split('.  ')[1].split(' (');
		 	return { category: significant[0], id: significant[1].split(')')[0] };

		});

		var json = JSON.stringify(lookup);

		fs.writeFile('cats.js', json, function (err) {
		  if (err) throw err;
		  console.log('It\'s saved!');
		});

});