getting a value from redis using node js

Question

What am I doing wrong in the code below? The left_label and right_label variables seem to always be "true", when I know I have them in the Redis set to some string. I'm assuming it's because the client.get function is successful and returns true, but how do I get it to return the actual value?

var http = require('http');
var redis = require('redis');
var client = redis.createClient(6379, 127.0.0.1);

var server = http.createServer(function (request, response) {

    var left_label = client.get('left', function(err, reply) {
        console.log(reply);
        return reply;
    });

    var right_label = client.get('right', function(err, reply) {
        console.log(reply);
        return reply;
    });

    response.writeHead(200, {"Content-Type": "text/html"});

    var swig  = require('swig');
    var html = swig.renderFile('/var/www/nodejs/index.html', {
        left: left_label,
        right: right_label
    });

    response.end(html);

});
server.listen(8000);
console.log("Server running at http://127.0.0.1:8000/");

redis access is asynchronous, reply has the actual value but left_label and right_label won't have it — mithril_knight
– mithril_knight, Commented Nov 19, 2015 at 13:40

Daniel B · Accepted Answer · 2015-11-19 13:56:56Z

The get call is asynchronous and must be handled that way.

A suggestion would be to combine it with a promise library such as bluebird as suggested in the NPM documentation for the redis module.

That way, we can promisify the redis module and use it in a more simple way.

var redis = require('redis');
bluebird.promisifyAll(redis.RedisClient.prototype);

and use the new async version of the get function, as below.

function getLabelValues(){
    var left_promise = client.getAsync("left").then(function(reply) {
        return reply;
    });

    var right_promise = client.getAsync("right").then(function(reply) {
        return reply;
    }); 

    return Promise.all([left_label, right_label]);
}

getLabelValues().then(function(results){
    //This is run when the promises are resolved
    //access the return data like below
    var left_label = results[0];
    var right_label = results[1];
});

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