How can I pretty-print JSON using node.js?

Question

This seems like a solved problem but I am unable to find a solution for it.

Basically, I read a JSON file, change a key, and write back the new JSON to the same file. All works, but I loose the JSON formatting.So, instead of:

{
  name:'test',
  version:'1.0'
}

I get

{name:'test',version:'1.1'}

Is there a way in Node.js to write well formatted JSON to file ?

`JSON.stringify` chokes on cyclic objects, and `util.inspect` doesn't produce valid json. :\ I found no [native] solution to pretty printing JSON in NodeJS — ThorSummoner, Jan 04 '17 at 00:47
@ThorSummoner: That is a problem with JSON, not with Node—JSON does not natively support cyclic references. There is a solution [here, in another question](https://stackoverflow.com/a/9382383/104184). — Sasha Chedygov, Mar 22 '18 at 21:46

score 1094 · Accepted Answer · edited Feb 09 '17 at 23:43

1094

JSON.stringify's third parameter defines white-space insertion for pretty-printing. It can be a string or a number (number of spaces). Node can write to your filesystem with fs. Example:

var fs = require('fs');

fs.writeFile('test.json', JSON.stringify({ a:1, b:2, c:3 }, null, 4));
/* test.json:
{
     "a": 1,
     "b": 2,
     "c": 3,
}
*/

See the JSON.stringify() docs at MDN, Node fs docs

edited Feb 09 '17 at 23:43

worc

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answered Apr 14 '11 at 23:34

Ricardo Tomasi

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Note : instead of 4, use `"\t"` if you want tabs. – Jeremy Thille Apr 01 '20 at 04:36
In latest nodejs you need to provide a callback function as third parameter, see this answer: https://stackoverflow.com/a/11677276/675065 – Alp Apr 23 '20 at 07:30
@Alp means the third parameter of `fs.writeFile`; you don't actually have to use the callback if the write is the last command in your script. You only need the callback if you want to do something after `writeFile`, other than exit the process. – jcollum Sep 29 '20 at 23:18

score 240 · Answer 2 · edited Mar 01 '14 at 08:53

240

I think this might be useful... I love example code :)

var fs = require('fs');

var myData = {
  name:'test',
  version:'1.0'
}

var outputFilename = '/tmp/my.json';

fs.writeFile(outputFilename, JSON.stringify(myData, null, 4), function(err) {
    if(err) {
      console.log(err);
    } else {
      console.log("JSON saved to " + outputFilename);
    }
});

edited Mar 01 '14 at 08:53

Alexey B.

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answered Jul 26 '12 at 20:10

nym

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4

Make sure the `tmp` folder exist or else this might fail. – Larry Battle Dec 06 '12 at 04:57
4

in most unix systems (including Mac & Linux..and if I recall BSD), `tmp` folder exists by default – Antony Jan 16 '13 at 20:28
what is the location(Output filename) to be given in case of windows – Devrath Jul 01 '13 at 11:47
I don't know why my file didn't get written (just opened empty) without the callback... Or maybe it's async, and it didn't work because I had an exception thrown while app startup? – Tomasz Gandor Sep 12 '17 at 23:05
1

Thanks, it helped me a lot. – Suraj Jain Feb 02 '18 at 10:08
1

@TomaszGandor: All I/O in Node is async by default, so the `writeFile` call doesn't block the program. If you don't pass a callback, Node doesn't have any more code to run, so it exits immediately after the call, likely before the actual write finished. – Sasha Chedygov Mar 22 '18 at 21:48
Thanks. This answer helps me! – Feng Liu Oct 31 '18 at 20:52

adius · Answer 3 · 2018-02-03T12:29:44.350

120

If you just want to pretty print an object and not export it as valid JSON you can use console.dir().

It uses syntax-highlighting, smart indentation, removes quotes from keys and just makes the output as pretty as it gets.

const jsonString = `{"name":"John","color":"green",
                     "smoker":false,"id":7,"city":"Berlin"}`
const object = JSON.parse(jsonString)

console.dir(object, {depth: null, colors: true})

Under the hood it is a shortcut for console.log(util.inspect(…)). The only difference is that it bypasses any custom inspect() function defined on an object.

edited Feb 03 '18 at 12:29

answered Nov 14 '15 at 10:04

adius

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console.dir doesn't produce valid json. – Gregg Lind Dec 30 '16 at 17:14
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@GreggLind Clarified that in the answer! – adius Feb 03 '18 at 12:30
This made my express server stall. I don't know why :( – Sanket Berde Sep 28 '18 at 11:10

score 53 · Answer 4 · answered Sep 28 '18 at 11:09

53

If you don't want to store this anywhere, but just view the object for debugging purposes.

console.log(JSON.stringify(object, null, "  "));

You can change the third parameter to adjust the indentation.

answered Sep 28 '18 at 11:09

Sanket Berde

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I've been looking for this solution -like for ever! The last param works like a charm! – vt2424253 Mar 21 '19 at 18:36

illvart · Answer 5 · 2020-12-12T03:20:55.517

35

I know this is old question. But maybe this can help you

JSON string

var jsonStr = '{ "bool": true, "number": 123, "string": "foo bar" }';

Pretty Print JSON

JSON.stringify(JSON.parse(jsonStr), null, 2);

Minify JSON

JSON.stringify(JSON.parse(jsonStr));

edited Dec 12 '20 at 03:20

answered Dec 05 '20 at 06:02

illvart

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score 29 · Answer 6 · edited Aug 08 '19 at 11:48

29

what about this?

console.table(object)

edited Aug 08 '19 at 11:48

Samuel Philipp

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answered Aug 08 '19 at 11:44

Panuwat Kulcharatyothin

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this is a good solution for small datasets, but for large, complex, deeply nested objects it's essentially impossible to read with all the line wrapping. there might be a solution to that too I suppose. – Matt Korostoff Dec 06 '21 at 19:59

score 4 · Answer 7 · answered Nov 16 '20 at 15:02

Another workaround would be to make use of prettier to format the JSON. The example below is using 'json' parser but it could also use 'json5', see list of valid parsers.

const prettier = require("prettier");
console.log(prettier.format(JSON.stringify(object),{ semi: false, parser: "json" }));

score -1 · Answer 8 · answered Mar 31 '22 at 10:02

-1

if prettify is name value pairs on new lines then specifying number of spaces in stringify didn't work for me the only thing that worked for me was

await fs.promises.writeFile('testdataattr.json',JSON.stringify(datatofile, null,'\r\n'),'utf8') ;

answered Mar 31 '22 at 10:02

GMC

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How can I pretty-print JSON using node.js?

8 Answers8

JSON string

Pretty Print JSON

Minify JSON

Linked