NodeJS: problem with request asynchronous, synchronous, api

Question

I have problem with trying to turn asynchronous function into synchronous.

here is a method from class:

doPost: function(call, data) {

    var uri = 'http://localhost/api/'+call;

    var api = http.createClient(80, 'localhost');

    var domain = 'localhost';

    var request = api.request("POST", uri,
                        {'host' : domain,
                         'Content-Type' : 'application/x-www-form-urlencoded', 
                         "User-Agent": this.userAgent,
                         'Content-Length' : data.length
                     });

    request.write(data);
    request.end();

    request.on('response', function (response) {  
        response.on ('data', function (chunk) {

            sys.puts(chunk);

            try {
                var result = JSON.parse(chunk);                    
                //------------ the problem

                return HOW_TO_RETURN_RESULT;

                //------------ /the problem
            }catch (err) {
                return {'ok': 0, 'err': err}
            }

        });
    });

},

Want to use this function in this way:

result = obj.doPost('getSomeData.php', '&data1=foo&data2=bar');

Reagards

Tom

Baggz · Accepted Answer · 2011-01-09 13:14:28Z

4

Simply use callback.

obj.doPost('getSomeData.php', '&data1=foo&data2=bar', function(data) {

  result = data;

});

answered Jan 9, 2011 at 13:14

Baggz

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1 Comment

Jakob Over a year ago

That does not turn it into a synchronous function. It does exactly the opposite of that. (But on the other hand, it is of course exactly how this function should be used).

Community · Accepted Answer · 2017-05-23 12:31:46Z

1

It is impossible to turn an asynchronous function into a synchronous one.

It simply cannot be done.

Instead, you must pass a callback to your function and receive the "return value" in async fashion.

In theory though, you could write some code to block your function from returning until some condition is met (ie, until the async operation is complete), but that would also require the program to be able do other things on another thread while the block is executing, which is probably not possible in node. And even if it were, it would be a world class antipattern and crime against node.js and all things evented and probably summon a velociraptor.

Conclusion: Learn how to work with asynchronous code. Also, you might be interested in reading this question/answer from yesterday (or at least the answer; the question is not very well phrased).

edited May 23, 2017 at 12:31

CommunityBot

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answered Jan 9, 2011 at 13:10

Jakob

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5 Comments

Tom Over a year ago

I read about "promises" in node.js but can't find any example that fit to my code.

Jakob Over a year ago

Promises are pretty much callbacks in disguise

Jakob Over a year ago

Also, even if promises did what you wanted them to, node.js doesn't have them: japhr.blogspot.com/2010/04/no-more-promises-in-nodejs.html

b_erb Over a year ago

They are now EventEmitters.

Tom Over a year ago

@Jakob thanks - I was fighting with asynchronous with no reason :)

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