Node.js — Write a JSON Object to a File

When working on a new feature or app idea, storing data on the file system can be a good solution. You can skip the database setup and save JSON to a file instead.

Node.js Series Overview

  1. String Replace All Appearances
  2. Remove All Whitespace From a String in JavaScript
  3. Generate a Random ID or String in Node.js or JavaScript
  4. Remove Extra Spaces From a String in JavaScript or Node.js
  5. Remove Numbers From a String in JavaScript or Node.js
  6. Get the Part Before a Character in a String in JavaScript or Node.js
  7. Get the Part After a Character in a String in JavaScript or Node.js
  8. How to Check if a Value is a String in JavaScript or Node.js
  9. Check If a String Includes All Strings in JavaScript/Node.js/TypeScript
  10. Check if a Value is a String in JavaScript and Node.js
  11. Limit and Truncate a String to a Given Length in JavaScript and Node.js
  12. Split a String into a List of Characters in JavaScript and Node.js
  13. How to Generage a UUID in Node.js
  14. Reverse a String in JavaScript or Node.js
  15. Split a String into a List of Lines in JavaScript or Node.js
  16. Split a String into a List of Words in JavaScript or Node.js
  17. Detect if a String is in camelCase Format in Javascript or Node.js
  18. Check If a String Is in Lowercase in JavaScript or Node.js
  19. Check If a String is in Uppercase in JavaScript or Node.js
  20. Get the Part After First Occurrence in a String in JavaScript or Node.js
  21. Get the Part Before First Occurrence in a String in JavaScript or Node.js
  22. Get the Part Before Last Occurrence in a String in JavaScript or Node.js
  23. Get the Part After Last Occurrence in a String in JavaScript or Node.js
  24. How to Count Words in a File
  25. How to Shuffle the Characters of a String in JavaScript or Node.js
  26. Append Characters or Words to a String in JavaScript or Node.js (Coming soon)
  27. Check if a String is Empty in JavaScript or Node.js (Coming soon)
  28. Ensure a String Ends with a Given Character in JavaScript or Node.js (Coming soon)
  29. Left-Trim Characters Off a String in JavaScript or Node.js (Coming soon)
  30. Right-Trim Characters Off a String in JavaScript or Node.js (Coming soon)
  31. Lowercase the First Character of a String in JavaScript or Node.js (Coming soon)
  32. Uppercase the First Character of a String in JavaScript or Node.js (Coming soon)
  33. Prepend Characters or Words to a String in JavaScript or Node.js (Coming soon)
  1. Get Number of Seconds Since Epoch in JavaScript
  2. Get Tomorrow’s Date in JavaScript
  3. Increase a Date in JavaScript by One Week
  4. Add Seconds to a Date in Node.js and JavaScript
  5. Add Month(s) to a Date in JavaScript or Node.js
  6. Add Week(s) to a Date in JavaScript or Node.js
  7. Get the Current Year in JavaScript or Node.js
  8. How to Get a UNIX Timestamp in JavaScript or Node.js
  9. How to Convert a UNIX Timestamp to a Date in JavaScript or Node.js
  10. Add Days to a Date in JavaScript or Node.js
  11. Get Yesterday's Date in JavaScript or Node.js
  12. Add Minutes to a Date in JavaScript or Node.js (Coming soon)
  13. Add Hours to a Date in JavaScript or Node.js (Coming soon)
  14. Check If a Date Is Today in JavaScript or Node.js (Coming soon)
  15. Check If a Date is Tomorrow in JavaScript or Node.js (Coming soon)
  16. Check If a Date is Yesterday in JavaScript or Node.js (Coming soon)
  17. How to Format a Date YYYY-MM-DD in JavaScript or Node.js (Coming soon)

Write JSON to File

JavaScript comes with the JSON class that lets you serialize an object to JSON with JSON.stringify. The file system fs module then writes data to the disk.

In the following, you’ll see examples for writing JSON to a file using callbacks and promises. Be careful with synchronous file operations in Node.js. The synchronous methods block the Node.js event loop and everything else has to wait for the file read/write.

With Callbacks

The first thing is to serialize data to JSON. Notice that JSON.stringify(data, null, 2) will add line breaks and indentation keeping the JSON human readable:

const Fs = require('fs')

function writeToFile (data, path) {  
  const json = JSON.stringify(data, null, 2)

  Fs.writeFile(path, json, (err) => {
    if (err) {
      console.error(err)
      throw err
    }

    console.log('Saved data to file.')
  })
}

The callback gives you a single error parameter. Add error handling for cases where the file writing process went wrong.

With Promises

You have multiple ways to use promises file system methods in Node.js:

The following example uses the fs-extra package providing the Node.js file system API with full promise support and methods like copy(), remove(), mkdirs().

const Fs = require('fs-extra')

async function writeToFile (path, data) {  
  const json = JSON.stringify(data, null, 2)

  try {
    await Fs.writeFile(path, json)
    console.log('Saved data to file.')
  } catch (error) {
    console.error(error)
  }
}

That’s it!

Read JSON From File

Retrieve data from a file and parse it to the JavaScript representation. Again, the examples will show you asynchronous methods using callbacks and promises and not the synchronous operations.

With Callbacks

Use fs.readFile to receive a file’s content. If you don’t specify the encoding, Node.js provides the data as a buffer.

The following example uses the utf8 encoding to retrieve the JSON string. Deserialize the JSON content to JavaScript with JSON.parse:

const Fs = require('fs')

function readFromFile (path) {  
  Fs.readFile(path, 'utf8', (err, json) => {
    if (err) {
      console.error(err)
      throw err
    }

    const data = JSON.parse(json)
    console.log(data)
  })
}

Remember to convert the JSON string to JavaScript. The formatted JSON strings and JavaScript objects look similar. Ensure you’re working with JavaScript and not JSON.

With Promises

Here’s the file read using promises with the help of fs-extra:

const Fs = require('fs-extra')

async function dataFromFile (path) {  
  try {
    const json = await Fs.readFile(path, 'utf8')
    const content = JSON.parse(json)
    console.log(content)
  } catch (error) {
    console.log(error)
  }
}

Again, parse the JSON content to JavaScript before moving on with other operations.

Enjoy coding & make it rock!


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