Comments Inside JSON Complete Guide With Examples

JSON, short for JavaScript Object Notation, is a lightweight data interchange format that is easy for humans to read and write and easy for machines to parse and generate. JSON is a text format that is completely language-independent but uses conventions that are familiar to programmers of the C family of languages, including C, C++, C#, Java, JavaScript, Perl, Python, and many others. Although JSON is based on JavaScript syntax, it is used widely across various programming languages and platforms.

One thing that a lot of developers find missing in JSON is the ability to add comments. Comments are an essential part of any code, as they help improve code readability and maintainability. In this blog post, we will discuss comments in JSON, their limitations, and some workarounds to overcome these limitations.

Why JSON Doesn't Support Comments

JSON was designed to be a data exchange format and not a programming language. Its primary purpose is to provide a simple and efficient way to transmit data between a server and a client or between different parts of an application. Since JSON is only meant for data representation, it omits certain features found in programming languages, such as comments.

The absence of comments in JSON is intentional to keep the format simple and easily readable. Comments can make JSON files more complex and harder to parse, which goes against the primary goal of JSON being a lightweight data interchange format.

JSON5 and Comments

JSON5 is an extension to JSON that aims to make it more human-friendly. One of the key features that JSON5 brings to the table is support for comments. JSON5 allows both single-line (//) and multi-line (/* */) comments, similar to those in JavaScript.

Here's an example of how comments can be added to a JSON5 file:

{
  // Single-line comment
  "name": "Alice",
  "age": 30,
  "isStudent": false,
  /* Multi-line comment
     explaining the purpose of
     this JSON object */
  "courses": ["math", "history", "chemistry"]
}

JSON5 is not natively supported in most programming languages and platforms but can be easily integrated using external libraries.

For example, in JavaScript, you can use the json5 library to parse JSON5 files:

const JSON5 = require('json5');

const jsonString = `
{
  // Single-line comment
  "name": "Alice",
  "age": 30,
  "isStudent": false,
  /* Multi-line comment
     explaining the purpose of
     this JSON object */
  "courses": ["math", "history", "chemistry"]
}`;

const parsedObj = JSON5.parse(jsonString);
console.log(parsedObj);

Workarounds for Adding Comments to JSON

While JSON itself does not support comments, there are some workarounds that you can use to include comments in your JSON files.

1. Using Dummy Keys

One simple way to add comments to JSON is by using dummy keys with descriptive names. Here's an example:

{
  "_comment": "This JSON object represents a person",
  "name": "Alice",
  "age": 30,
  "isStudent": false,
  "_comment_courses": "List of courses the person is enrolled in",
  "courses": ["math", "history", "chemistry"]
}

This approach has its drawbacks, as these dummy keys will be treated as regular keys by the parser, and you need to make sure that they don't conflict with actual keys in your JSON structure.

2. Using External Files for Comments

Another approach is to maintain a separate file for comments, where you can document your JSON files. This method keeps your JSON files clean and prevents any parsing issues that may arise due to comments.

For example, you can create a .md or .txt file with the same name as your JSON file and document your JSON structure with comments there.

3. Converting JSON to YAML

YAML (short for "YAML Ain't Markup Language") is another data serialization format that is often used for configuration files and data exchange between languages with different data structures. YAML is a superset of JSON and supports comments using the # symbol.

Here's an example of a YAML file with comments:

# This YAML object represents a person
name: Alice
age: 30
isStudent: false
# List of courses the person is enrolled in
courses:
  - math
  - history
  - chemistry

You can convert your JSON files to YAML and use a YAML parser in your programming language to read the data with comments.

FAQ

Q: Can I use JavaScript comments in JSON files?

A: No, JSON does not support comments. You can use JSON5, an extension to JSON, which allows JavaScript-style comments or consider using one of the workarounds mentioned above.

Q: Is there any performance impact of using dummy keys for comments in JSON?

A: While using dummy keys as comments in JSON can affect performance slightly, it is generally negligible for small to moderately-sized JSON files. However, for large JSON files, it's better to consider other alternatives like JSON5 or maintaining external files for comments.

Q: Can I use YAML instead of JSON for my projects?

A: Yes, you can use YAML as an alternative to JSON, as it is a superset of JSON and supports additional features like comments. However, you need to make sure that the libraries and platforms you use in your projects support YAML.

Q: How can I convert my JSON files to JSON5?

A: Converting JSON files to JSON5 is straightforward, as JSON5 is mostly backwards-compatible with JSON. You can copy your JSON content to a JSON5 file and start adding comments as needed. Make sure to use a JSON5 parser in your programming language to read the JSON5 files.

In conclusion, JSON's lack of support for comments can be a challenge for developers who value code readability and maintainability. However, by using alternatives like JSON5 or the workarounds mentioned above, you can include comments in your JSON files and improve their clarity. Happy coding!