Making the while loop synchronous

Question

I've got a following piece of code

var page = 2; var last_page = 100; while(page <= last_page) {   request("http://some_json_server.com/data?page=" + page, function (error, response, body) {     if (!error && response.statusCode == 200) {       store_data(body)     }     page++;   });                 } 

I've done the following, but it is actually not retrieving anything. Am I doing this correctly?

var page = 2; var last_page = 100; while(page <= last_page) { var async_arr = []; async_arr.push(   function(next) {     request("http://some_api_url?page=" + page, function (error, response, body) {       if (!error && response.statusCode == 200) {         store_data(body);       }     });   } );  async.series(   async_arr, done ); 

Answer 1

With while you get a busy loop, which is counter-purpose in Node.

Make it a recursive function instead. Each call will be done in a separate tick.

var page = 2; var last_page = 100;  (function loop() {     if (page <= last_page) {         request("/data?page=" + page, function (error, response, body) {             if (!error && response.statusCode == 200) {                 store_data(body)             }             page++;             loop();         });     } }()); 

Answer 2

You're looking for async.whilst(). This solution is assuming you actually want to do each request after the other. As @UpTheCreek mentions (edit: the comment I referred to was edited) it would likely be possible to do it asynchronously and keep track of each result using async.parallel.

var page = 2,     lastPage = 100;  async.whilst(function () {   return page <= lastPage; }, function (next) {   request("http://some_json_server.com/data?page=" + page, function (error, response, body) {     if (!error && response.statusCode == 200) {       store_data(body)     }     page++;     next();   }); }, function (err) {   // All things are done! });