write a javascript object to a file in node

Question

How do I use Node to take a JS object (e.g. var obj = {a: 1, b: 2}) and create a file that contains that object?

For example, the following works:

var fs = require('fs')

fs.writeFile('./temp.js', 'var obj = {a: 1, b: 2}', function(err) {
  if(err) console.log(err)
  // creates a file containing: var obj = {a: 1, b: 2}
})

But this doesn't work:

var obj = {a: 1, b: 2}

fs.writeFile('./temp.js', obj, function(err) {
  if(err) console.log(err)
  // creates a file containing: [object Object]
})

Update: JSON.stringify() will create a JSON object (i.e. {"a":1,"b":2}) and not a Javascript object (i.e. {a:1,b:2})

I don't believe stringify is the answer. This will create a JSON string (i.e. {"a":1,"b":2}) and not a JS object (i.e. {a:1,b:2}) — Ed Williams
– Ed Williams, Commented Feb 9, 2017 at 9:48

Community · Accepted Answer · 2017-05-23 12:24:25Z

17

Thanks Stephan Bijzitter for the link

My problem can be solved like so:

var fs = require('fs')
var util = require('util')
var obj = {a: 1, b: 2}

fs.writeFileSync('./temp.js', 'var obj = ' + util.inspect(obj) , 'utf-8')

This writes a file containing: var obj = { a: 1, b: 2 }

edited May 23, 2017 at 12:24

CommunityBot

11 silver badge

answered Feb 9, 2017 at 10:09

Ed Williams

2,5073 gold badges18 silver badges22 bronze badges

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

1 Comment

Steve Dodier-Lazaro Over a year ago

This is unfortunately not a proper answer, as util.inspect will truncate arrays and integers, and not result in the expected object.

Mykola Borysyuk · Accepted Answer · 2017-02-09 09:14:02Z

3

Its because of arguments that writeFile requires.

https://nodejs.org/api/fs.html#fs_fs_writefile_file_data_options_callback

It wants data to be <String> | <Buffer> | <Uint8Array>

So your first example works because it's a string.

In order to make second work just use JSON.stringify(obj);

Like this

fs.writeFile('file.txt', JSON.stringify(obj), callback)

Hope this helps.

answered Feb 9, 2017 at 9:14

Mykola Borysyuk

3,4211 gold badge22 silver badges24 bronze badges

Comments

Emeke Ajeh · Accepted Answer · 2021-02-02 18:01:07Z

1

const fs = require('fs')
const util = require('util')
const obj = {a: 1, b: 2}

fs.writeFileSync(
  './temp.js',
  util.formatWithOptions({compact: false}, 'var obj = %o', obj),
  'utf-8'
)

Formatted output:

// ./temp.js
var obj = {
  a: 1,
  b: 2
}

edited Feb 2, 2021 at 18:01

answered Feb 2, 2021 at 17:49

Emeke Ajeh

1,0501 gold badge11 silver badges16 bronze badges

Comments

Robby Cornelissen · Accepted Answer · 2017-02-09 09:13:10Z

0

You need to stringify your object:

var obj = {a: 1, b: 2}

fs.writeFile('./temp.js', JSON.stringify(obj), function(err) {
  if(err) console.log(err)
})

answered Feb 9, 2017 at 9:13

Robby Cornelissen

98.6k23 gold badges154 silver badges180 bronze badges

Collectives™ on Stack Overflow

write a javascript object to a file in node

4 Answers 4

1 Comment

Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

1 Comment

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related