Understanding the Importance of Object vs. Array in JSON.stringify with Node.js

---

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Problem when using JSON.stringify in NodeJS

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---

The Scenario: Modifying a JSON File

Imagine you have a JSON file that starts off empty, containing only an empty array []. Your goal is to read this file, check for a specific array, and add items to it if it doesn't exist. You might write something like this:

[[See Video to Reveal this Text or Code Snippet]]

However, as soon as you try to modify randomJsonObject by adding a new array called "something", you encounter an unexpected result. Logging randomJsonObject gives you the correct structure, yet when you use JSON.stringify(randomJsonObject), it logs an empty array again.

Example Code Snippet

Here's what your attempts might look like:

[[See Video to Reveal this Text or Code Snippet]]

The Problem: Arrays vs. Objects

The root of the issue lies in the fact that the variable randomJsonObject is an array instead of an object. In the code, an array does not have the property "something". As a result, when you try to check the existence of randomJsonObject["something"], it returns undefined, leading to unexpected behavior.

What's Happening Under the Hood?

When you initially read the JSON file, you parse the contents into an array.

The modification method you used (randomJsonObject["something"]) works with the property of an object, not the elements of an array.

Hence, when you try to log the object as a JSON string, it doesn’t output what you expect.

The Solution: Correctly Initialize Your JSON Structure

To resolve this issue, you should begin by treating randomJsonObject as an object rather than an array. Before adding any new values, you can define it like so:

[[See Video to Reveal this Text or Code Snippet]]

Then, you can safely perform your checks and modifications. Your updated code should look something like this:

[[See Video to Reveal this Text or Code Snippet]]

Writing Back to the File

Once you've correctly structured your JSON, you can write it back to the file without issues:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion