function returning values as undefined in nodejs

Question

function returning values as undefined in nodejs

I am working on a NodeJs project for the first time. And now i am stuck with the function returning values through JS and getting values to use in express.

var dbitems = "before fn";
function refreshData(callback) {
        db.open(function (err, db) {
            if (!err) {
                db.collection('emp').find().toArray(function (err, items) {
                    dbitems = items;
                    callback(JSON.stringify(items));
                });
            }
            else {
                console.log("Could not be connnected" + err);
                dbitems = {"value":"not found"};
            }
        });

    }
}


refreshData(function (id) { console.log(id); });

This function retrieves values perfectly from refreshData and writes into console. But what I need is to use the retrieved value to send into express html file from this function by "returnedData"

exports.index = function (req, res) {
    var valrs = refreshData(function (id) {
        console.log(JSON.parse(id)); ---this again writes data perfectly in the console
    });
    console.log(valrs); -------------------but again resulting in undefined
    res.render('index', { title: 'Express test', returnedData: valrs });
};

Any help would be appreciated.

Thanks & Regards, Luckyy.

node.js
mongodb
callback

Answer 1

You need to render this after the database request finishes.. so it needs to be called from within the callback.

exports.index = function (req, res) {
    refreshData(function (id) {
        res.render('index', { title: 'Express test', returnedData: JSON.parse(id) });
    });
};

it's asynchronous so you can't just put values in order, needs to go through the callbacks.