var async = require('async');
var request = require('request');


app.get('endpoint',function(req, res){
    async.series([
        function(callback){request.get('url',callback)},
        function(callback){request.get('url2',callback)},
        function(callback){request.get('url'3,callback)},
    ],
    function(err,results){
        //handle error

        //results is an array of values returned from each one
        var processedData = {
            a: results[0],
            b: results[1],
            c: results[2]
        };
        res.send(processedDAta)
    })

})

app.get('/endpoint',function(req, res){
    var dataSources = ['url1', 'url2',url3];
    var requestData = [];

    processRequestData = function(){
    //do you stuff here
    res.send(processedData);
    };
    dataSources.forEach(function(dataSource){
        request.get(dataSource,function(err,result){
            //handle error

            requestData.push(result);
            if(requestData.length == dataSources.length){
                processRequestData();
            }
        })
    })
});

app.get('/resource', function(req, res){
    // object to send back in the response
    var results = {};

    // helper function to make requests and handle the data to results object
    var getData = function(url, propertyName, next){
      http.get(url, function(err, data){
        // let async.js know if there is an error
        if(err) return next(err);
        // save data to results object
        results[propertyName] = data;
        // async.js needs us to notify it when each operation is complete - so we call the callback without passing any data back to
        next();
      });
    };

    // array of operations to execute in series or parallel
    var operations = [];

    operations.push(function(next){
        getData('http://url-one', 'users', next);
    });

    operations.push(function(next){
    getData('http://url-two', 'posts', next);
    });

    // async.js has a few options on how to execute your operations - here we use series
    async.series(operations, function(err){
        if(err){
            throw err;
        }
        // if we get to this point, all of the operations have exectued and called
        // next() without any errors - send the response with a populated results object.
        res.send(results);
    });

});