# How to read and write a JSON object to a file in Node.js

By Atta Ur Rehman Shah (https://attacomsian.com/about). Published Mar 28, 2020, updated Oct 1, 2022. Topics: Node.js.
Canonical URL: https://attacomsian.com/blog/nodejs-write-json-object-to-file

> Learn how to write as well as read a JSON object from a file by using the Node.js file system module.

Sometimes you want to store a [JSON](https://attacomsian.com/blog/what-is-json) object to a file in a Node.js application and then retrieve it later. For example, when you are creating a new RESTful API, storing data on the local file system can be a good choice. You can skip the database setup and save JSON data to a file.

In this article, you'll learn how to **write a JSON object to file** in Node.js. In my previous article, we looked at how to [read and write files in Node.js](https://attacomsian.com/blog/reading-writing-files-nodejs). If you need more information about reading and writing files, take a look at it.

## Write JSON to File

JavaScript provides a built-in `JSON` object for parsing and serializing JSON data. You can use the [JSON.stringify()](https://attacomsian.com/blog/json-parse-stringify#jsonstringify) method to convert your JSON object into its string representation, and then use the file system `fs` module to write it to a file.

Here is an example that uses the `fs.writeFile()` method to asynchronously write a JSON object to a file:

```javascript
const fs = require('fs')

// create a JSON object
const user = {
  id: 1,
  name: 'John Doe',
  age: 22
}

// convert JSON object to a string
const data = JSON.stringify(user)

// write JSON string to a file
fs.writeFile('user.json', data, err => {
  if (err) {
    throw err
  }
  console.log('JSON data is saved.')
})
```

To [pretty-print the JSON object](https://attacomsian.com/blog/javascript-pretty-print-json) to the file, you can pass extra parameters to `JSON.stringify()`:

```javascript
// pretty-print JSON object to string
const data = JSON.stringify(user, null, 4)
```

The `fs` module also provides a method called `writeFileSync()` to write data to a file synchronously:

```javascript
try {
  fs.writeFileSync('user.json', data)
  console.log('JSON data is saved.')
} catch (error) {
  console.error(err)
}
```

Be careful when you use synchronous file operations in Node.js. The synchronous methods block the Node.js event loop and everything else has to wait for the file operation to be completed.

## Read JSON from File

To retrieve and parse JSON data from a file back to a JSON object, you can use the `fs.readFile()` method along with [JSON.parse()](https://attacomsian.com/blog/json-parse-stringify#jsonparse) for deserialization like below:

```javascript
const fs = require('fs')

// read JSON object from file
fs.readFile('user.json', 'utf-8', (err, data) => {
  if (err) {
    throw err
  }

  // parse JSON object
  const user = JSON.parse(data.toString())

  // print JSON object
  console.log(user)
})
```

The above example will output the following on the console:

```json
{ id: 1, name: 'John Doe', age: 22 }
```

Just like the `fs.writeFileSync()` method, you can also use `fs.readFileSync()` to read a file synchronously in a Node.js application. 

Take a look how to [read and write JSON files in Node.js](https://attacomsian.com/blog/nodejs-read-write-json-files) tutorial to learn more about reading and writing JSON files in a Node.js application.