I've been having some troubles with parsing JSON that is received with WebSocket (original question - Parse JSON received with WebSocket results in error). The JSON string itself is valid (tested with several JSON validators), but JSON.parse throws an exception. I am trying to figure out what is it exactly that it cannot parse, but the only thing I'm getting is "SyntaxError: unexpected_token ILLEGAL", it doesn't say where is the exact position of the failed token. Is there any way of extracting such information?

Update: If I copy-paste that JSON string to a static file (e.g. "data.json") and then retrieve it and parse it with the same function (JSON.parse) - then it works fine. So I'm assuming there's something tricky going on, I thought of newline symbol (may be there was \n instead of \r\n or vice versa) but pletely removing all the line breaks didn't help. I would think that it very well may be an encoding problem, but the data is received via websocket and according to documentation it's utf-8 string.

2nd Update: IT WORKS just fine if I use "json_parse" from here: .js Then it works fine! Does that mean this is a bug in "JSON.parse" implementation used by Chrome or what?

Thank you.

I've been having some troubles with parsing JSON that is received with WebSocket (original question - Parse JSON received with WebSocket results in error). The JSON string itself is valid (tested with several JSON validators), but JSON.parse throws an exception. I am trying to figure out what is it exactly that it cannot parse, but the only thing I'm getting is "SyntaxError: unexpected_token ILLEGAL", it doesn't say where is the exact position of the failed token. Is there any way of extracting such information?

Update: If I copy-paste that JSON string to a static file (e.g. "data.json") and then retrieve it and parse it with the same function (JSON.parse) - then it works fine. So I'm assuming there's something tricky going on, I thought of newline symbol (may be there was \n instead of \r\n or vice versa) but pletely removing all the line breaks didn't help. I would think that it very well may be an encoding problem, but the data is received via websocket and according to documentation it's utf-8 string.

2nd Update: IT WORKS just fine if I use "json_parse" from here: https://github./douglascrockford/JSON-js/blob/master/json_parse.js Then it works fine! Does that mean this is a bug in "JSON.parse" implementation used by Chrome or what?

Thank you.

• javascript
• parsing
• json

• 3 Try jslint? And if it's not 'private' data, post the bad json here. – Marc B Commented Aug 19, 2011 at 15:32
• Better than jslint is jsonlint – epascarello Commented Aug 19, 2011 at 15:43
• Returns "JSON: good.", jsonlint says it's valid too. Even I copy-paste it from my web-page back to JSON.parse - it parses the string. Please see the "Update". – stepan Commented Aug 19, 2011 at 15:46
• I am facing this issue while receiving the string from Websockets too. My string is as simple as {"s":\"t\"}. Removing the backslashes fixes the problem. Can anyone help me with this? – shadyabhi Commented Mar 10, 2013 at 16:02

4 Answers 4

You could copy an implementation of JSON.parse() from somewhere (like out of jQuery), change it's name so you can call it directly, tweak the implementation so that it never detects the built-in parser so it always uses the JS parser and then change your code to use the new JS version of the parser, then trace through it in a javascript debugger until you find what it doesn't like.

One thing to check is if you have quotes and slashes within your JSON string. If yes, they need to be escaped:

{
    "key": "i've \"quotes\" in me",
    "key2": "and \\slashes too"
}

Also, JSONLint gives you the exact location of the error.

As per JSON, you cannot have quotes and slashes in your strings, so you need to escape them.

I think you don't need to call JSON.parse:

JSON.parse({"key": "whatever"}) // Syntax Error ILLEGAL

because it's already an object. I would also be curious to see the result of the following code:

eval("(" + json + ")");

Or

JSON.parse(decodeURIComponent(json));

Can't tell much with the details, but the possibility may be that your validator is doing non-strict parsing and your javascript may be doing strict parsing...