CODEWITHSUNDEEP
node.jsasynchronous
Prachi g
Prachi g

Reputation: 839

Calling synchronously in node.js

I have the following method:

var get = function(query_para,callback) {

    var queryParams = query_para;
    var timestamp ;
    var some_Data = {};
    var data;

    request({url:"http://some-url.com/q?", qs:queryParams}, function(err, response, body) {
        if(err) { console.log(err); return; }
        console.log(body);
        var data = JSON.parse(body);

        some_Data.count = data.count; 

        console.log("Returned data: "+some_Data.count);

         callback(null,some_Data);
    });

};

I want to call this method twice and combine their results. I have implemented it using callbacks in a following way:

get({ start: '2014/09/13-10:00:00', end: '2014/09/13-11:00:00', format: 'json' }, function(err, result1){
    get({ start: '2014/09/13-11:00:00', end: '2014/09/13-12:00:00', format: 'json' }, function(err, result2){
        console.log("r1:: "+result1.count);
        console.log("r2:: "+result2.count);
    });
});

Is there any better way to make it synchronous? I read about a few things (promises and sync-client), but I didn't understand. What is the best way to call that function twice and combine their results?

Upvotes: 1

Views: 68

Answers (1)

Patrick
Patrick

Reputation: 6958

First of all, it doesn't look like your code is synchronous. I would suggest to leave it asynchronous and use promise library like Q. First, make sure Q is installed:

npm install q

From your get function, return a promise:

var get = function(query_para) {

    var queryParams = query_para;
    var timestamp ;
    var some_Data = {};
    var data;
    //Use q
    var Q = require("q");

    //define a deferred that will be resolved later
    var deferred = Q.defer();

    request({url:"http://some-url.com/q?", qs:queryParams}, function(err, response, body) {
        if(err) { console.log(err); return; }
        console.log(body);
        var data = JSON.parse(body);

        some_Data.count = data.count; 

        console.log("Returned data: "+some_Data.count);

        //resolve the deferred here
        deferred.resolve(some_Data);
    });

    //return the promise
    return deferred.promise;
};

From your code that calls the get function:

var q = require("q");
var promiseArr = [];
//First promise to your get function
promiseArr.push(get({ start: '2014/09/13-10:00:00', end: '2014/09/13-11:00:00', format: 'json'}));
//Second promise
promiseArr.push(get({ start: '2014/09/13-11:00:00', end: '2014/09/13-12:00:00', format: 'json' }));

//Use q.all to call a callback when all promises in the array are resolved:
q.all(promiseArr).then(function (results) {
   //First item is the data resolved from the first promise in the array
   console.log("r1:: "+results[0].count);
   //Second item is data resolved from second promise
   console.log("r2:: "+results[1].count);
});

Upvotes: 2

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