Any way to make a generic response handler in nodejs?

Question

Any way to make a generic response handler in nodejs?

I'm trying to write a couple of endpoints that will make GET and POST http requests to various backend services, the format of data is all going to be very similar so responseHandler function will be copied over and over to different route function, I wonder if there is a way to externalize responseHandler for reuse. I tried to just move it out, but then I would lose reference to res. Anyone has any tips on a more modular design?

routes['/endpoint'] = function(req, res){
    console.log("Serving endpoint: /endpoint")
    var params={"param": "param-value"}

    var options = {
      host: 'localhost',
      path: '/service?param='+params.param,
      method: 'GET'
    };

    var responseHandler = function(response) {
      var data = '';

      // keep track of the data you receive
      response.on('data', function(chunk) {
        data += chunk + "\n";
      });

      // finished? ok, send the data to the client in JSON format
      response.on('end', function() {
            res.header("Content-Type:","application/json");
            res.end(data);
      });
    };

    // make the request, and then end it, to close the connection
    http.request(options, responseHandler).end();
};

javascript
node.js

Answer 1

generally i would think you could create a folder in your lib called responseHandlers, add a file that contains something like

var responseHandler = function(response) {
  var data = '';

  // keep track of the data you receive
  response.on('data', function(chunk) {
    data += chunk + "\n";
  });

  // finished? ok, send the data to the client in JSON format
  response.on('end', function() {
        res.header("Content-Type:","application/json");
        res.end(data);
  });
};
exports.Handler = responseHandler;

save that as whateverHandler.js, then create an index.js file that requires whatever.js and exports it Handler. this way if you need to add more handlers in the future you just have to add a file and update the index.js. to use, do something in the route handler like

var handler = require('./lib/responseHandlers').whateverHandler;
routes['/endpoint'] = function(req, res){
    console.log("Serving endpoint: /endpoint")
    var params={"param": "param-value"}

    var options = {
      host: 'localhost',
      path: '/service?param='+params.param,
      method: 'GET'
    };
};

// make the request, and then end it, to close the connection
http.request(options, handler).end();
};

Answer 2

You could turn responseHandler into a function generator, and pass in your res object so you don't lose it:

var responseHandler = function(res) {
  return function(response) {
    var data = '';

    // keep track of the data you receive
    response.on('data', function(chunk) {
      data += chunk + "\n";
    });

    // finished? ok, send the data to the client in JSON format
    response.on('end', function() {
          res.header("Content-Type:","application/json");
          res.end(data);
    });
  };
}

And use it like this:

routes['/endpoint'] = function(req, res){
    console.log("Serving endpoint: /endpoint")
    var params={"param": "param-value"}

    var options = {
      host: 'localhost',
      path: '/service?param='+params.param,
      method: 'GET'
    };

    // make the request, and then end it, to close the connection
    http.request(options, responseHandler(res)).end();
};