Parsing JSON in node.js gives an Error

Question

My Node.js application reads a string, containing JSON data, from a Python backend using GET method. Sometimes when I use JSON.parse() and refresh the page after it succeeds, it gives an Unexpected token , error.

[
      {
       "postid":"c4jgud85mhs658sg4hn94jmd75s67w8r",
       "email":"[email protected]",
       "post":"hello world",
       "comment":[]
      },
      {
       "postid":"c4jgud85mhs658sg4hn94jmd75s67w8r",
       "email":"[email protected]",
       "post":"hello world",
       "comment":[]
      }
]

By console.logging the JSON object, I was able to verify that it only prints the object partially (meaning that only a part of the object was passed) when it gives the error - for example:

4hn94jmd75s67w8r",
       "email":"[email protected]",
       "post":"hello world",
       "comment":[]
      }
]

or

[
      {
       "postid":"c4jgud85mhs658sg

In node.js, Im only using

var data = JSON.parse(resJSON); //resJSON is the variable containing the JSON

You're missing a double quote at the end of comment in the first object. — mscdex
– mscdex, Commented Oct 20, 2014 at 1:04
Can you share the Node.js code that handles the response of the GET request? — Jonathan Lonowski
– Jonathan Lonowski, Commented Oct 20, 2014 at 1:10
Please share relevant code, as well as the full error message; "Invalid token" must precede something like "expected xx instead of yy" — Gui Imamura
– Gui Imamura, Commented Oct 20, 2014 at 1:12

Jonathan Lonowski · Accepted Answer · 2014-10-20 01:42:30Z

3

If it's succeeding "sometimes," I'd suspect you're parsing the response as the 'data' arrives, such as:

http.get('...', function (res) {
    res.on('data', function (data) {
        console.log(JSON.parse(data.toString()));
    });
});

This will work if the response is sent all at once. But, it can also be divided into multiple chunks that will be received through multiple 'data' events.

To handle chunked responses, you'll want to combine the chunks back together and parse the response as a whole once the stream has come to an 'end'.

http.get('...', function (res) {
    var body = '';

    res.on('data', function (chunk) {
        body += chunk.toString();
    });

    res.on('end', function () {
        console.log(JSON.parse(body));
    });
});

edited Oct 20, 2014 at 1:42

answered Oct 20, 2014 at 1:33

Jonathan Lonowski

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