An introduction to using Redis in Node.js applications_node.js

Before starting this article, please make sure to install Redis and Node.js and the Redis extension for Node.js - node_redis

First create a new folder and create a new text file app.js. The content of the file is as follows:

var redis = require("redis")
  , client = redis.createClient();
 
client.on("error", function (err) {
  console.log("Error " + err);
});
 
client.on("connect", runSample);
 
function runSample() {
  // Set a value
  client.set("string key", "Hello World", function (err, reply) {
    console.log(reply.toString());
  });
  // Get a value
  client.get("string key", function (err, reply) {
    console.log(reply.toString());
  });
}

After connecting to Redis, the runSample function will be called and a value will be set, and then the value will be read out. The results of the operation are as follows:

OK
Hello World

We can also use the EXPIRE command to set the expiration time of the object. The code is as follows:

var redis = require('redis')
  , client = redis.createClient();
 
client.on('error', function (err) {
  console.log('Error ' + err);
});
 
client.on('connect', runSample);
 
function runSample() {
  // Set a value with an expiration
  client.set('string key', 'Hello World', redis.print);
  // Expire in 3 seconds
  client.expire('string key', 3);
 
  // This timer is only to demo the TTL
  // Runs every second until the timeout
  // occurs on the value
  var myTimer = setInterval(function() {
    client.get('string key', function (err, reply) {
      if(reply) {
        console.log('I live: ' + reply.toString());
      } else {
        clearTimeout(myTimer);
        console.log('I expired');
        client.quit();
      }
    });
  }, 1000);
}

Note: The timer used above is only to demonstrate the EXPIRE command. You must use timers with caution in Node.js projects.

The output of running the above program is:

Reply: OK
I live: Hello World
I live: Hello World
I live: Hello World
I expired

Next we check how long a value persists before it expires:

var redis = require('redis')
  , client = redis.createClient();
 
client.on('error', function (err) {
  console.log('Error ' + err);
});
 
client.on('connect', runSample);
 
function runSample() {
  // Set a value
  client.set('string key', 'Hello World', redis.print);
  // Expire in 3 seconds
  client.expire('string key', 3);
 
  // This timer is only to demo the TTL
  // Runs every second until the timeout
  // occurs on the value
  var myTimer = setInterval(function() {
    client.get('string key', function (err, reply) {
      if(reply) {
        console.log('I live: ' + reply.toString());
        client.ttl('string key', writeTTL);
      } else {
        clearTimeout(myTimer);
        console.log('I expired');
        client.quit();
      }
    });
  }, 1000);
}
 
function writeTTL(err, data) {
  console.log('I live for this long yet: ' + data);
}

Run result:

Reply: OK
I live: Hello World
I live for this long yet: 2
I live: Hello World
I live for this long yet: 1
I live: Hello World
I live for this long yet: 0
I expired