Sliding window epiration of keys in Redis

app.js

// Prerequisites:
// 		npm install redis

var redis = require('redis');
var client = redis.createClient();

client.setex('fixedexpkey', 5, 'Foo');
client.setex('slidingexpkey', 5, 'Bar');

// Get value every second without using a sliding window expiration implementation
setInterval(getStatic, 1000);
// Get value every second using custom sliding windows expiration implementation
setInterval(getSliding, 1000);

function getStatic() {
	client.get('fixedexpkey', function(err, val) {
		if (!err) {
			console.log('fixedexpkey =', val);
		}
	});
}

function getSliding() {
	getex('slidingexpkey', 5, function(err, val) {
 		if (!err) {
 			console.log('slidingexpkey =', val);
 		}
 	});
}

// Sample implementation of a sliding window expiration
// NOTE: You could argue that in reallity you don't need to
//       GET and EXPIRE your key within a transaction (MULTI)
//	 Most of the time you would probably be fine without
function getex(key, seconds, callback) {
	var multi = client.multi();
	multi.get(key);
	multi.expire(key, seconds);
	multi.exec(function(err, replies) {
		if (err) {
			callback(err);
		} else {
			callback(null, replies[0]);
		}
	});
}