Waiting till call back completes Node.js

Question

Waiting till call back completes Node.js

My situation is like this, I have a server like this and inside I am calling another callback function which gets multiple values:

var http = require('http'); 
var server = http.createServer(req,resp) {
     var finalVal = "";

     consumer.on('message',function(message) {
         finalVal = message;
         console.log(finalVal);
     });

     resp.end(finalVal);
});

My finalVal should display all the multiple values it fetches and send it as a response, but problem is it's sending only first value where as console.log displays all the values. I do understand that by the time consumer.on ends response would have committed. Can someone please help me how to handle this scenario since I'm very new to Node.js ? Currently due to heavy deadlines I don't have time to read full information about callbacks. But defnitely I would take time to learn about callbacks.

Edit: Here consumer.on calls multiple times till it fetches all the data from backend, I need to send all those data in a final response. I am using node-kafka to consume to kafka messages.

javascript
node.js

Answer 1

There must be an end event or something like that which tells that consumer has finished the message, you can use that

I am not sure what is consumer here, but in most of cases we go with something like bellow

var finalVal = '';

consumer.on('message',function(message) {
     finalVal += message; // So on each message you will just update the final value
     console.log(finalVal);
 });

consumer.on('end',function(){ // And at the end send the response
     resp.end(finalVal);
});