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Read and write a JSON file in Node.js

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Learn how to load json files into Node JS to change and save them - including code examples and a Codepen demo.

27 Mar, 2020 · 3 min read

Ever needed to load, write and save a file in node.js? Of course, I've heard of databases, but sometimes writing a small JSON file is easier. 🔥

Creating a basic node.js app

To read and write files in node.js, we need to include the file system package in our application.

First, we will create a basic application to test this. Open up your terminal and execute the following command.

Read more: Basic Node.js Express application

Note: Ensure you have node.js installed on your machine. See nodejs website for the installation procedure.

mkdir fs-app && cd fs-app && npm init

This will create a directory called fs-app, make the terminal change into this directory, and then execute the npm init function.

npm init will create a default starting app for node.js.

Now we need to create our application index file. Open your favorite terminal and create an index.js file.

Installing the file system package in node.js

To install the package, all we have to include in our index.js file is the following code:

const fs = require('fs');

All this tells our application we are planning to use the fs package. Now we can load JSON files, add changes and save them again.

Read a JSON file in Node JS

To read a file, we will start by creating our demo file. Create a file called people.json and place the following content in it.

{
  "people": [
    {
      "firstname": "Chris",
      "lastname": "Bongers"
    }
  ]
}

Now we add the following code to our index.js

let rawdata = fs.readFileSync('people.json');
let people = JSON.parse(rawdata);
console.log(people);

If we now run node index.js in our terminal, we should see our JSON object logged out. 👏

Write JSON data to a file in node.js

To write data back to the file, we will manipulate the contents of our JSON object, let's add another person, and now save it to the JSON file.

people.people.push({
  firstname: 'Steve',
  lastname: 'Jobs',
});

fs.writeFileSync('people.json', JSON.stringify(people));

We use people.people because our index in the JSON file is called people and the object we created. Then we tell the fs package to write to the people.json file the newly adjusted object.

Now, if we rerun node index.js and open our people.json file, we should see two entries!

Congrats, you just read and wrote a JSON file in node.js.

You can find this project on GitHub

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