Node.js Nested Callbacks, multiple requests

Question

I'm making requests to Parse.com to 3 different objects that are needed to render a View. I'd like to know what's the general/best approach in cases like these in which there are multiple requests before actually handling the data.

Code:

    var Parse = require('parse-api').Parse;
    var parse = new Parse();

    exports.single = function() {
        parse.find('Class_1',params1,function(error,response1){
            parse.find('Class_2',params2,function(error, response2){
                parse.find('Class_3',params3,function(error3, response3){

                    // handle responses....
                    // render view....
                })
            })
        })
    }

Thanks!

Answer 1

Use Step.js or async.js to make this look cleaner. Step.js is simpler, but async.js gives you more flexibility.

Also, your function single needs to have a callback, and cannot return values since the functions it's invoking are not returning values.

Additionally, generally the data retrieval methods should be separate from the rendering methods.

With Step.js, this could look like:

 var Parse = require('parse-api').Parse,
    Step = require('step');
    var parse = new Parse();
exports.getAndRenderData = function(res, params1, params2, params3){
   getData(params1, params2, params3, function(err, data){
      if(err)
        throw err:
      else {
        res.render('viewname', data);
      }
   });
}

var getData = function(params1, params2, params3, callack) {
    var data = {}; 
    Step()(
        function getClass1(){
            parse.find('Class_1',params1, this);
        },
        function getClass2(err, class1data){
           if (err) throw err;
           data.class1 = class1data;
           parse.find('Class_2',params2, this);
        },
        function getClass3(err, class2data){
           if (err) throw err;
           data.class2 = class2data;
           parse.find('Class_3',params3, this);
        },
        function callbackWithAll(err, class3data){
           if (err) callback(err); 
           else {
             data.class3 = class3data;
             callback(null, data);
           }
        }
    );
}