JS Exception Stack: Parsing JSON

Question

I have been battling this issue for half a week to no avail, my problem is:

using Node.js 0.10.12 to parse JSON files like so:

var invalidJson = '{ this is bad }';



try {
    JSON.parse( invalidJson );
}

catch (exc) {
    console.log(exc.stack);
    throw exc;
}

the output:

SyntaxError: Unexpected token t
    at Object.parse (native)
    at Object.<anonymous> (test.js:7:10)
    ...
    at node.js:901:3

test.js:12
    throw exc;

..And then a duplicate of 'SyntaxError: Unexpected token t..' because I re-throw the exception

Now, when doing:

JSON.parse( invalidJson );

without try {} catch {}

I get this error:

undefined:1
{ this is bad }
  ^
SyntaxError: Unexpected token t
    at Object.parse (native)
    at Object.<anonymous> (test.js:17:6)
    ...
    at node.js:901:3

this error message tells me exactly where the JSON parsing broke. When the JSON file is large, it's virtually impossible to locate the error without these details.

How can I forward this descriptive error message in my custom try{}catch{} exception handler?

thanks!

Unfortunatly I haven't found any solution yet, but someone did. I'm using this online tool to check JSON errors jsoneditoronline.org — Fabio C.
– Fabio C., Commented Apr 28, 2016 at 15:55

Esailija · Accepted Answer · 2013-08-05 15:06:43Z

1

Well even with:

$ node --builtins-in-stack-traces test.js

And test.js:

var invalidJson = '{ this is bad }';

//Make err.stack return an array of CallSite objects instead of string
Error.prepareStackTrace = function(_, stack) {
    return stack;
};


try {
    JSON.parse( invalidJson );
}

catch (exc) {
    var asd = exc.stack;
}

asd.forEach( function(v){
    console.log((v.getMethodName() || v.getFunctionName()) +
         ":" + v.getLineNumber());
});

The output is:

MakeGenericError:118
MakeSyntaxError:324
parse:56
null:9
_compile:456
.js:474
load:356
_load:312
runMain:497
startup:119

Doesn't seem possible from Javascript, you should file a bug to expose the JSON line number information to JS since they are obviously accessing it when doing the ^--- thing. JSON should not be hand written so syntax errors shouldn't be common unless the JSON serializer being used is somehow broken.

answered Aug 5, 2013 at 15:06

Esailija

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2 Comments

Rafael Vega Over a year ago

"JSON should not be hand written". Really? What's an option for writing config files?

Ryan Schumacher Over a year ago

@RafaelVega I think the point is that JSON is very verbose and prone to syntax errors. While something like YAML is less verbose, more readable, a subset of JSON and the js-yaml will give descriptive syntax issues.

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