Example 1-6. Using asynchronous code to write and read a file in Node.js

var fs = require('fs');
var timestamp = new Date().toString();

fs.writeFile('date.txt', timestamp, function (err) {
	if (err) throw err;

	fs.readFile('date.txt', function (err, contents) {
		if (err) throw err;
		console.log('Checking the contents'); // 2
		console.assert(contents == timestamp); // 3
	});
});

console.log('I am the last line of the script'); // 1

// Console output:
// I am the last line of the script
// Checking the contents