First of all, the issue in your question is that, inside the for loop, client.get is invoked with an asynchronous callback where the synchronous for loop will not wait for the asynchronous callback and hence the next line res.json({data:jobs}); is getting called immediately after the for loop before the asynchronous callbacks. At the time of the line res.json({data:jobs}); is getting invoked, the array jobs is still empty [] and getting returned with the response.

To mitigate this, you should use any promise modules like async, bluebird, ES6 Promise etc.

Modified code using async module,

app.get('/jobs', function (req, res) {

    var jobs = [];

    client.keys('*', function (err, keys) {

        if (err) return console.log(err);

        if(keys){

            async.map(keys, function(key, cb) {

               client.get(key, function (error, value) {

                    if (error) return cb(error);

                    var job = {};

                    job['jobId']=key;

                    job['data']=value;

                    cb(null, job);

                }); 

            }, function (error, results) {

               if (error) return console.log(error);

               console.log(results);

               res.json({data:results});

            });

        }

    });

});

But from the Redis documentation, it is observed that usage of
Keys are intended for debugging and special operations, such as
changing your keyspace layout and not advisable to production
environments.

Hence, I would suggest using another module called redisscan as below which uses SCAN instead of KEYS as suggested in the Redis documentation.

Something like,

var redisScan = require('redisscan');

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





redisScan({

        redis: redis,

        each_callback: function (type, key, subkey, value, cb) {

            console.log(type, key, subkey, value);

            cb();

        },

        done_callback: function (err) {

            console.log(-=-=-=-=-=--=-=-=-);

            redis.quit();

        }

    });