Please explain why JSON.stringify output differs from toString output in this short example

Question

This looks similar to console.log inconsistent with JSON.stringify, but: I'd like to know what exactly happens behind the screen, because I can't understand what exactly happens here, and why JSON.stringify() does not show the error text. Here's my code (saved in firstio.js)

var fs = require('fs')

try {
  var file = fs.readFileSync(process.argv[2])
}
catch(error) {
  console.log(error.toString());
  console.log(JSON.stringify(error, null, 2));
  process.exit()
}
console.log(file.toString().split("\n").length - 1)

when run as follows: node firstio.js the output is as follows:

TypeError: path must be a string
{}

If JSON.stringify is converting the error object where is the error text that toString() apparently can find?

When it is run as follows: node firstio.js nonexistingfile the output is:

Error: ENOENT, no such file or directory 'nonexistingfile'
{
  "errno": -2,
  "code": "ENOENT",
  "path": "nonexistingfile",
  "syscall": "open"
}

stringify process enumarable properties. Maybe error does not have any. — Radek Pech
– Radek Pech, Commented Mar 2, 2016 at 13:08
Ok, while searching for a PHP-like var_dump() for Javascript, the top answers here on SO mentioned JSON.stringify(), but - as I found and wondered about - that does not work for the error variable. Turns out that is the answer: the error variable is not an enumerable object. Thanks @Radek Pech. I'll mark your answer. Which still leaves the question does JS have a var_dump() equivalent. No it does not, though console.dir() seems to come close. — raarts
– raarts, Commented Mar 2, 2016 at 13:42

Community · Accepted Answer · 2017-05-23 12:07:51Z

1

Method JSON.stringify() process objects based on their enumarable properties.

But window.Error object does not have any enumerable properties thus JSON.stringify(error) returns only empty object.

You can write an error directly into console:

console.log(new Error('Something happened'));

Which will output Error: Something happened.

Or you can write your own method to stringify error; see Is it not possible to stringify an Error using JSON.stringify?

edited May 23, 2017 at 12:07

CommunityBot

11 silver badge

answered Mar 3, 2016 at 9:57

Radek Pech

3,1081 gold badge27 silver badges31 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Please explain why JSON.stringify output differs from toString output in this short example

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related