Parsing JSON data from a URL

Question

I'm trying to create function that can parse JSON from a url. Here's what I have so far:

function get_json(url) {
    http.get(url, function(res) {
        var body = '';
        res.on('data', function(chunk) {
            body += chunk;
        });

        res.on('end', function() {
            var response = JSON.parse(body);
                return response;
        });
    });
}

var mydata = get_json(...)

When I call this function I get errors. How can I return parsed JSON from this function?

What, no URL? How are we supposed to help you with this problem? — Brad
– Brad, Commented Oct 18, 2013 at 2:28
Your return response; won't be of any use. You can pass a function as an argument to get_json, and have it receive the result. Then in place of return response;, invoke the function. So if the parameter is named callback, you'd do callback(response);. — user2736012
– user2736012, Commented Oct 18, 2013 at 2:29

Mauricio Gracia Gutierrez · Accepted Answer · 2014-06-18 20:11:39Z

13

In case someone is looking for an solution that does not involve callbaks

    function getJSON(url) {
        var resp ;
        var xmlHttp ;

        resp  = '' ;
        xmlHttp = new XMLHttpRequest();

        if(xmlHttp != null)
        {
            xmlHttp.open( "GET", url, false );
            xmlHttp.send( null );
            resp = xmlHttp.responseText;
        }

        return resp ;
    }

Then you can use it like this

var gjson ;
gjson = getJSON('./first.geojson') ;

answered Jun 18, 2014 at 20:11

Mauricio Gracia Gutierrez

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Comments

user2736012 · Accepted Answer · 2013-10-18 02:31:14Z

Your return response; won't be of any use. You can pass a function as an argument to get_json, and have it receive the result. Then in place of return response;, invoke the function. So if the parameter is named callback, you'd do callback(response);.

// ----receive function----v
function get_json(url, callback) {
    http.get(url, function(res) {
        var body = '';
        res.on('data', function(chunk) {
            body += chunk;
        });

        res.on('end', function() {
            var response = JSON.parse(body);
// call function ----v
            callback(response);
        });
    });
}

         // -----------the url---v         ------------the callback---v
var mydata = get_json("http://webapp.armadealo.com/home.json", function (resp) {
    console.log(resp);
});

Passing functions around as callbacks is essential to understand when using NodeJS.

hexacyanide · Accepted Answer · 2013-10-18 02:30:31Z

5

The HTTP call is asynchronous, so you must use a callback in order to fetch a resultant value. A return call in an asynchronous function will just stop execution.

function get_json(url, fn) {
  http.get(url, function(res) {
    var body = '';
    res.on('data', function(chunk) {
      body += chunk;
    });

    res.on('end', function() {
      var response = JSON.parse(body);
      fn(response);
    });
  });
};

get_json(url, function(json) {
  // the JSON data is here
});

In this example, function(json) {} is passed into the get_json() function as fn(), and when the data is ready, fn() is called, allowing you to fetch the JSON.

answered Oct 18, 2013 at 2:30

hexacyanide

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