Accessing field on Json Object in Node.js

Question

So I'm new to JavaScript programming. I'm getting this JSON payload on a POST request:

{
  "subscriptionId" : "asdasdasdasd",
  "originator" : "localhost",
  "contextResponses" : [
    {
      "contextElement" : {
        "type" : "",
        "isPattern" : "false",
        "id" : "id",
        "attributes" : [
          {
            "name" : "temperature",
            "type" : "int",
            "value" : "5"
          }
        ]
      },
      "statusCode" : {
        "code" : "200",
        "reasonPhrase" : "OK"
      }
    }
  ]
}

And using this code to try and access a certain field:

var qs = require('querystring');
var http = require('http');
http.createServer(function (req, res) {
var obj;

if (req.method == 'POST') {
        var body = '';
        req.on('data', function (data) {
            body += data;
            console.log(body.attributes.value);
            if (body.length > 1e6)
                req.connection.destroy();
        });

        req.on('end', function () {
            var post = qs.parse(body);
            // use post['blah'], etc.
        });
    }
}).listen(8087, "188.???.??.???");
console.log('Server running at http://188.???.??.???:8087/');

As you can see I'm trying to access the value field and trying to retrieve the number 5. Obviously, it's not working. I tried googleing it and this is probably something really silly. Any suggestions on how to access the field?

EDIT:

The data from console.log(body):

Server running at http://????????
{
  "subscriptionId" : "asdasdasdasd",
  "originator" : "localhost",
  "contextResponses" : [
    {
      "contextElement" : {
        "type" : "",
        "isPattern" : "false",
        "id" : "fiwaresensorfinal",
        "attributes" : [
          {
            "name" : "temperature",
            "type" : "int",
            "value" : "5"
          }
        ]
      },
      "statusCode" : {
        "code" : "200",
        "reasonPhrase" : "OK"
      }
    }
  ]
}

The console.log(data):

<Buffer 7b 0a 20 20 22 73 75 62 73 63 72 69 70 74 69 6f 6e 49 64 22 20 3a 20 22 35 35 38 31 37 62 33 62 39 38 61 64 64 31 38 63 63 33 65 31 38 33 62 65 22 2c 0a ...>

The console.log(recv):

{ subscriptionId: '55817b3b98add18cc3e183be',
  originator: 'localhost',
  contextResponses: [ { contextElement: [Object], statusCode: [Object] } ] }

there's no property called attributes at the top level and by adding ´´ to the data you are turning it in to a string — Rune FS, Jun 17 '15 at 17:06
What do you suggest doing? I used this answer's code: http://stackoverflow.com/questions/4295782/how-do-you-extract-post-data-in-node-js — Diogo Nunes, Jun 17 '15 at 17:09
I suggest that you dont convert it to a string and then payattentuon to what the properties are called from the top level to the value you need — Rune FS, Jun 17 '15 at 17:13

TaoPR · Accepted Answer · 2015-06-17T17:58:46.480

1

Since data is returned as a string by http module, you need to parse your received data to JSON object first:

Instead of :

req.on('data', function (data) {
        body += data;
        console.log(body.attributes.value);
        ....
});

Do this:

req.on('data', function (data) {
        var recv = JSON.parse(data);
        console.log(recv.contextResponses[0].contextElement.attributes[0].value);
        ....
});

If your data received as a response from the server is as you posted in the first paragraph, then you can access the value via .contextResponses[0].contextElement.attributes[0].value.

edited Jun 17 '15 at 17:58

answered Jun 17 '15 at 17:12

TaoPR

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Thanks for the quick answer. I tryed that code but it gave me: TypeError: Cannot read property 'value' of undefined :\ – Diogo Nunes Jun 17 '15 at 17:15
It was a typo error and I have now updated the answer. Please see. – TaoPR Jun 17 '15 at 17:16
Thanks again! But now it's getting: TypeError: Cannot read property '0' of undefined. – Diogo Nunes Jun 17 '15 at 17:22
I think the data you posted is probably not the actual response. Can you please update your question with what `console.log(data)` says? – TaoPR Jun 17 '15 at 17:23
Answer updated! I used body instead of data and it still gives me that error! – Diogo Nunes Jun 17 '15 at 17:33
You sir are a genious! Thank you :) – Diogo Nunes Jun 17 '15 at 19:16

Accessing field on Json Object in Node.js

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