Synchronous Requests in Node js

Question

How could I make the  request  module in Node js load things in a synchronous fashion  The best advice I ve seen is to somehow use the callback to get the function to not return itself until it is done  I am trying to use the  request  function inline in code  things need to be processed based on that data that can t be placed in callbacks    So how could I use the callback of the  request  module to keep it from returning itself until it is finished with loading the resource   What I m doing is running a loop that downloads two values from an API  and then has to do some math based on those values  While the math could be done in callbacks    the loop would advance without the values it needs to perform the next operation   So stopping the loop from advancing until the data is ready would solve the issue          loop                  URL Generation          request   url  base   u ext   function  err  res  body             var split1   body split   n            var split2   split1 1  split                ucomp   split2 1                request   url  base   v ext   function  err  res  body             var split1   body split   n            var split2   split1 1  split                vcomp   split2 1                   math which needs to be after functions get variables and before loop advances

User · Answer

You can do something exactly similar with the request library, but this is sync using const https = require('https'); or const http = require('http');, which should come with node.

Here is an example,

const https = require('https');

const http_get1 = {
    host : 'www.googleapis.com',
    port : '443',
    path : '/youtube/v3/search?arg=1',
    method : 'GET',
    headers : {
        'Content-Type' : 'application/json'
    }
};

const http_get2 = {
host : 'www.googleapis.com',
    port : '443',
    path : '/youtube/v3/search?arg=2',
    method : 'GET',
    headers : {
        'Content-Type' : 'application/json'
    }
};

let data1 = '';
let data2 = '';

function master() {

    if(!data1)
        return;

    if(!data2)
        return;

    console.log(data1);
    console.log(data2);

}

const req1 = https.request(http_get1, (res) => {
    console.log(res.headers);

    res.on('data', (chunk) => {
        data1 += chunk;
    });

    res.on('end', () => {
        console.log('done');
        master();
    });
});


const req2 = https.request(http_get2, (res) => {
    console.log(res.headers);

    res.on('data', (chunk) => {
        data2 += chunk;
    });

    res.on('end', () => {
        console.log('done');
        master();
    });
});

req1.end();
req2.end();

User · Answer

The short answer is  don t        You really can t  And that s a good thing  I d like to set the record straight regarding this  NodeJS does support Synchronous Requests  It wasn t designed to support them out of the box  but there are a few workarounds if you are keen enough  here is an example  var request   require  sync-request        res1  res2  ucomp  vcomp   try       res1   request  GET   base   u ext       res2   request  GET   base   v ext       ucomp   res1 split   n   1  split       1       vcomp   res2 split   n   1  split       1       doSomething ucomp  vcomp      catch  e      When you pop the hood open on the  sync-request  library you can see that this runs a synchronous child process in the background  And as is explained in the sync-request README it should be used very judiciously  This approach locks the main thread  and that is bad for performance  However  in some cases there is little or no advantage to be gained by writing an asynchronous solution  compared to the certain harm you are doing by writing code that is harder to read   This is the default assumption held by many of the HTTP request libraries in other languages  Python  Java  C  etc   and that philosophy can also be carried to JavaScript  A language is a tool for solving problems after all  and sometimes you may not want to use callbacks if the benefits outweigh the disadvantages  For JavaScript purists this may rankle of heresy  but I m a pragmatist so I can clearly see that the simplicity of using synchronous requests helps if you find yourself in some of the following scenarios   Test Automation  tests are usually synchronous by nature    Quick API mash-ups  ie hackathon  proof of concept works etc    Simple examples to help beginners  before and after     Be warned that the code above should not be used for production  If you are going to run a proper API then use callbacks  use promises  use async await  or whatever  but avoid synchronous code unless you want to incur a significant cost for wasted CPU time on your server

User · Answer

See sync-request  https   github com ForbesLindesay sync-request  Example   var request   require  sync-request    var res   request  GET    http   example com    console log res getBody

User · Answer

In 2018  you can program the  usual  style using async and await in Node js   Below is an example  that wraps request callback in a promise and then uses await to get the resolved value   const request   require  request        wrap a request in an promise function downloadPage url        return new Promise  resolve  reject    gt            request url   error  response  body    gt                if  error  reject error               if  response statusCode    200                    reject  Invalid status code  lt     response statusCode     gt                               resolve body                             now to program the  usual  way    all you need to do is use async functions and await    for functions returning promises async function myBackEndLogic         try           const html   await downloadPage  https   microsoft com           console log  SHOULD WORK             console log html               try downloading an invalid url         await downloadPage  http          com         catch  error            console error  ERROR             console error error               run your async function myBackEndLogic

User · Answer

You can use retus to make cross-platform synchronous HTTP requests   const retus   require  retus     const   body     retus  https   google com        gt    lt  doctype html gt        That s it

User · Answer

You should take a look at library called async  and try to use async series call for your problem

User · Answer

Though asynchronous style may be the nature of node js and generally you should not do this  there are some times you want to do this   I m writing a handy script to check an API and want not to mess it up with callbacks   Javascript cannot execute synchronous requests  but C libraries can   https   github com dhruvbird http-sync

User · Answer

Aredridels answer is relatively good  upvoted it   but I think it lacks the loop equivalent  This should help you   Sync code equivalent   while  condition      var data   request url      lt math here gt    return result    Async code for serial execution   function continueLoop       if   condition  return cb result     request url  function err  res  body         lt math here gt      continueLoop          continueLoop

User · Answer

The short answer is  don t  If you want code that reads linearly  use a library like seq  But just don t expect synchronous  You really can t  And that s a good thing   There s little or nothing that can t be put in a callback  If they depend on common variables  create a closure to contain them  What s the actual task at hand   You d want to have a counter  and only call the callback when the data is there   var waiting   2  request   url  base   u ext   function  err  res  body         var split1   body split   n        var split2   split1 1  split            ucomp   split2 1       if --waiting    0  callback         request   url  base   v ext   function  err  res  body         var split1   body split   n        var split2   split1 1  split            vcomp   split2 1       if --waiting    0  callback         function callback            do math here      Update 2018  node js supports async await keywords in recent editions  and with libraries that represent asynchronous processes as promises  you can await them  You get linear  sequential flow through your program  and other work can progress while you await  It s pretty well built and worth a try

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