JSON Explained: Basics, Syntax, and Practical Usage for Developers

By 佐川 直弘 | Naohiro Sagawa (運営者)

※記事内に広告を含みます。Amazonアソシエイトとして適格販売により収入を得ています。　

1. What Is JSON? Understanding the Data Format from the Basics

Definition and Core Concept of JSON

JSON is a text-based data format that represents information primarily using key–value pairs. This structure is highly suitable for exchanging data between programs.

For example, user information can be expressed in JSON as follows.

{
  "name": "Sato",
  "age": 30,
  "email": "sato@example.com"
}

In this example, the keys are name, age, and email, each mapped to a corresponding value. This makes the data easy for humans to read and efficient for computers to process.

Key Features and Advantages of JSON

1. Lightweight and Simple

• JSON is a compact format that avoids unnecessary information, making it efficient for data transmission and storage.

1. High Readability

• Compared to XML or binary formats, JSON is visually easy to understand, which simplifies debugging and maintenance.

1. Language-Independent

• JSON is supported by many programming languages, including JavaScript, offering high compatibility across platforms.

1. Object-Oriented Friendly

• JSON is designed around object-based structures, making it a natural fit for object-oriented programming.

Why JSON Became Widely Adopted

Because JSON is based on JavaScript object syntax, it rapidly became a standard data format in web application development.

In particular, JSON is widely used for data exchange in REST APIs due to its simplicity and compatibility. Compared to XML, JSON requires less code and can be parsed faster, making it ideal for mobile applications and cloud services.

Common Use Cases of JSON

1. API Requests and Responses

• JSON is widely used as a data exchange format between web services. For example, weather APIs commonly return data in JSON format.

1. Configuration Files

• JSON is often used to store application settings, such as configuration files like config.json.

1. Data Storage and Databases

• NoSQL databases such as MongoDB use JSON-based formats as their data model.

1. Data Analysis and Log Management

• JSON is also used for analytics and error logging, as its structured format simplifies data parsing.

Summary

JSON is a lightweight and simple data exchange format that is widely adopted across programming languages, databases, and APIs. Due to its readability and flexibility, it is used by both beginners and advanced developers.

In the next section, we will explore JSON syntax in greater detail, using real code examples to deepen your understanding.

2. Basic JSON Syntax and Structure

Core Structure of JSON

JSON is built on key–value pairs as its fundamental elements. Data is written using curly braces {}, as shown below.

Example: JSON Representing User Information

{
  "name": "Sato",
  "age": 30,
  "email": "sato@example.com",
  "isMember": true
}

• Keys (e.g., "name", "age") must always be written as strings.
• Values can be strings, numbers, booleans, null, arrays, or objects.

Data Types and Examples

1. String

• Must be enclosed in double quotes.
• Example:
  "title": "Introduction to JSON"

1. Number

• Both integers and floating-point numbers are supported.
• Example:
  "price": 1999, "discount": 9.5

1. Boolean

• Specified as true or false.
• Example:
  "isAvailable": true

1. null

• Indicates the absence of a value.
• Example:
  "nickname": null

1. Array

• Lists of values are expressed using square brackets [].
• Example:
  "tags": ["JSON", "Data Format", "Programming"]

1. Object

• Objects can be nested within other objects.
• Example:
  "address": { "city": "Tokyo", "zip": "100-0001" }

Important Rules When Writing JSON

1. Always Use Double Quotes

• Keys and string values must be enclosed in double quotes. Single quotes will cause errors.

1. No Trailing Commas Allowed

• Adding a trailing comma to the last element in an array or object results in an error.
• Invalid example:
  { "name": "Sato", "age": 30, }

1. Comments Are Not Supported

• Standard JSON does not allow comments. Documentation should be written separately, such as in a README file.

Summary

JSON enables efficient data management using key–value pairs, arrays, and objects. Its simple yet flexible structure makes it ideal for data exchange and storage.

3. Practical Examples of JSON Usage

Data Exchange via APIs

JSON is widely used as a data exchange format between servers and web or mobile applications. In REST APIs in particular, JSON is commonly adopted as the standard format for requests and responses.

Example: API to Retrieve User Information

• Request

  GET /users/1 HTTP/1.1
  Host: example.com
  Accept: application/json

• Response

  HTTP/1.1 200 OK
  Content-Type: application/json

  {
    "id": 1,
    "name": "Sato",
    "email": "sato@example.com",
    "status": "active"
  }

Using JSON as a Configuration File

JSON is also used as a configuration format for applications.

Example: Configuration File (config.json)

{
  "server": {
    "host": "localhost",
    "port": 3000
  },
  "database": {
    "user": "admin",
    "password": "password123",
    "dbname": "exampledb"
  },
  "logging": {
    "level": "info",
    "enabled": true
  }
}

Data Communication Between Frontend and Backend

JSON is frequently used in asynchronous communication with AJAX or the Fetch API.

Example: Fetching Data with the Fetch API (JavaScript)

fetch('https://api.example.com/users/1')
  .then(response => response.json())
  .then(data => {
    console.log(data.name); // Displays "Sato"
  })
  .catch(error => console.error('Error:', error));

Using JSON in Databases (NoSQL)

NoSQL databases store and manage data in JSON-based formats.

Example: Saving Data in MongoDB

{
  "_id": ObjectId("507f1f77bcf86cd799439011"),
  "name": "Tanaka",
  "age": 28,
  "skills": ["JavaScript", "Python"]
}

Summary

JSON is an essential format in many scenarios, including API communication, configuration files, databases, and log management.

4. How to Work With and Process JSON

Parsing and Generating JSON in JavaScript

Parsing JSON

const jsonString = '{"name": "Tanaka", "age": 25, "isMember": true}';
const user = JSON.parse(jsonString);

console.log(user.name);  // Output: Tanaka

Generating JSON (Serialization)

const user = {
  name: "Tanaka",
  age: 25,
  isMember: true
};

const jsonString = JSON.stringify(user, null, 2);
console.log(jsonString);

Working With JSON in Other Programming Languages

Python Example

import json

json_str = '{"name": "Sato", "age": 28}'
data = json.loads(json_str)
print(data['name'])  # Output: Sato

Error Handling

JavaScript Example

try {
  const data = JSON.parse('{name: "Sato"}'); // Error occurs
} catch (error) {
  console.error('JSON parsing error:', error.message);
}

Summary

Because JSON is easy to parse and generate, it enables efficient data management in many applications.

5. Advanced Uses of JSON and Modern Technologies

Data Validation with JSON Schema

JSON Schema is a specification used to define and validate the structure and format of JSON data.

Example: Schema for User Information

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "title": "User Information",
  "type": "object",
  "properties": {
    "name": {
      "type": "string"
    },
    "age": {
      "type": "integer",
      "minimum": 0
    },
    "email": {
      "type": "string",
      "format": "email"
    }
  },
  "required": ["name", "email"]
}

Structured Data with JSON-LD

JSON-LD provides semantically enriched data for search engines and is widely used for SEO optimization.

Example: Structured Company Information

{
  "@context": "https://schema.org",
  "@type": "Organization",
  "name": "Sample Corporation",
  "url": "https://www.example.com",
  "contactPoint": {
    "@type": "ContactPoint",
    "telephone": "+81-90-1234-5678",
    "contactType": "customer service"
  }
}

Latest Specifications and Extended Technologies

Example: JSON5

{
  name: "Tanaka", // Comments are allowed
  age: 30,
  skills: ["JavaScript", "Python",], // Trailing commas are allowed
}

Summary

JSON supports a wide range of advanced use cases, including validation and SEO optimization, making it a highly versatile data format.

6. Comparing JSON with Other Data Formats

JSON vs XML

Example: JSON

{
  "user": {
    "name": "Sato",
    "age": 30
  }
}

Example: XML

<user>
  <name>Sato</name>
  <age>30</age>
</user>

Comparison Table

JSON vs YAML

Example: JSON

{
  "name": "Sato",
  "age": 30
}

Example: YAML

name: Sato
age: 30

Comparison Table

Summary

JSON excels in simplicity and speed, making it ideal for data management and API communication.

7. The Future of JSON and Emerging Trends

Standardization and Evolution of JSON

JSON is standardized under RFC 8259 and uses UTF-8 as its default encoding.

The Emergence of JSON5

JSON5 is an extended specification that introduces more flexible syntax and support for comments.

JSON5 Example

{
  name: "Tanaka",
  age: 25, // Comments are allowed
}

JSON-LD and the Semantic Web

JSON-LD supports SEO enhancement and semantic data annotation, enabling structured data for search engines.

Future Challenges

• Performance: Migration toward binary formats such as BSON.
• Security: Improved escaping mechanisms and validation tools.

Summary

JSON continues to evolve alongside modern technologies and plays a central role in data management systems.

8. Summary and Additional Resources

Key Takeaways

• JSON is widely adopted as a simple and efficient data exchange format.
• It is used in APIs, configuration files, and SEO-related structured data.
• Integration with modern technologies and security measures continues to advance.

Additional Resources

• Official JSON Website – Specifications and basic rules of JSON.
• JSONLint – A JSON syntax validation tool.
• MDN Web Docs – JSON documentation for JavaScript.

Next Steps and Practical Advice

1. Use JSON in small-scale projects to gain hands-on experience.
2. Learn advanced techniques such as JSON Schema and JSON-LD.
3. Stay updated with the latest trends through developer communities and forums.

Summary

JSON streamlines data management and continues to expand its capabilities when combined with modern technologies.

FAQ: Frequently Asked Questions About JSON

1. What is JSON?

A: JSON (JavaScript Object Notation) is a text-based data exchange format designed to represent data in a simple and efficient way.

• It consists of key–value pairs that clearly express data structure.
• It is lightweight and supported by many programming languages, making it ideal for APIs and configuration files.

2. What is JSON commonly used for?

A: JSON is used in the following scenarios.

1. API Communication: Sending and receiving data between clients and servers.
2. Configuration Files: Storing application and tool settings.
3. Databases: Managing data in NoSQL databases such as MongoDB.
4. Log Management: Recording error logs and debugging information.
5. Structured Data: Using JSON-LD for SEO optimization.

3. What data types does JSON support?

A: JSON supports the following six data types.

1. String: "name": "Sato"
2. Number: "age": 30
3. Boolean: "isMember": true
4. null: "nickname": null
5. Array: "skills": ["JavaScript", "Python"]
6. Object: "address": {"city": "Tokyo", "zip": "100-0001"}

4. What is the difference between JSON and XML?

A: The key differences between JSON and XML are shown below.

5. How is JSON different from YAML?

A: YAML is a human-friendly data format that differs from JSON in the following ways.

6. Which programming languages support JSON?

A: JSON is supported by many programming languages.

• JavaScript: Uses JSON.parse() and JSON.stringify().
• Python: Uses the json module.
• PHP: Uses json_decode() and json_encode().
• Java: Uses libraries such as Jackson or Gson.

7. Can comments be added to JSON?

A: Standard JSON does not support comments. However, the following alternatives are commonly used.

1. Adding a comment-only key:

{
  "_comment": "This setting is for debugging",
  "debug": true
}

2. Using JSON5: JSON5 supports comments.

8. How should JSON errors be handled?

A: Below is an example of handling JSON-related errors.

JavaScript Example:

try {
  const data = JSON.parse('{name: "Sato"}'); // Error occurs
} catch (error) {
  console.error('JSON parsing error:', error.message);
}

9. Can JSON be converted to a binary format?

A: Yes. BSON (Binary JSON) is a binary-optimized format derived from JSON.

• It is commonly used in NoSQL databases such as MongoDB.
• It provides faster and more efficient data processing.

10. What are the latest trends and technologies related to JSON?

A: Recent JSON-related technologies include the following.

1. JSON-LD: Structured data for SEO optimization.
2. JSON5: An extended specification with flexible syntax and comment support.
3. GraphQL: An API design approach that exchanges data in JSON format.
4. Serverless Architectures: Event-driven data processing using platforms such as AWS Lambda and Google Cloud Functions.

Summary

This FAQ covered both fundamental and advanced topics related to JSON. While JSON is simple and easy to use, careful handling of syntax errors and extended specifications is sometimes required. Use this article and FAQ as a reference to master JSON from basics to advanced applications and apply it effectively in real-world projects.