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beginner Phase · HTTP and Web Fundamentals

JSON

Master JSON as the standard data format for API communication.

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What is JSON?

JSON (JavaScript Object Notation) is the standard data format for API communication. It's lightweight, human-readable, and easy to parse.

JSON Syntax

{
  "string": "hello",
  "number": 42,
  "float": 3.14,
  "boolean": true,
  "null": null,
  "array": [1, 2, 3],
  "object": {
    "nested": "value"
  }
}

JSON Data Types

Type Example Notes
String "hello" Double quotes required
Number 42, 3.14 No distinction between int/float
Boolean true, false Lowercase
Null null Represents absence
Array [1, 2, 3] Ordered list
Object {"key": "val"} Key-value pairs

JSON in API Communication

# Request
POST /api/users HTTP/1.1
Content-Type: application/json

{
  "name": "Alice",
  "email": "alice@example.com",
  "preferences": {
    "theme": "dark",
    "notifications": true
  }
}

# Response
HTTP/1.1 201 Created
Content-Type: application/json

{
  "id": 123,
  "name": "Alice",
  "email": "alice@example.com",
  "createdAt": "2026-08-15T10:30:00Z"
}

JSON Best Practices

  1. Use consistent naming — camelCase or snake_case (pick one)
  2. Always include Content-Type: application/json
  3. Use ISO 8601 for dates — "2026-08-15T10:30:00Z"
  4. Return meaningful error responses — Include error code and message
  5. Never return sensitive data — Passwords, tokens, secrets

JSON vs XML

Feature JSON XML
Readability High Medium
Size Smaller Larger
Parsing Easier Complex
Schema JSON Schema XSD
API Usage REST, GraphQL SOAP, legacy

Best Practices

Key Principles

  1. Follow SOLID principles
  2. Write clean, readable code
  3. Test thoroughly
  4. Document decisions
  5. Monitor in production

Implementation

  • Start simple, refactor as needed
  • Use established patterns
  • Consider trade-offs
  • Review with peers

Continuous Improvement

  • Learn from incidents
  • Update documentation
  • Share knowledge
  • Mentor others

Key Points

  • Understanding JSON is essential for production systems
  • Always consider scalability and maintainability
  • Test thoroughly before deploying to production
  • Monitor performance and set up alerting

Common Patterns

  1. Validation: Always validate input at the boundary
  2. Error Handling: Use structured error responses
  3. Logging: Log key events for debugging
  4. Testing: Unit, integration, and load tests
  5. Documentation: Keep docs updated with code changes

Practice Problems

0 / 3 solved
Implement JSON

Design and implement a solution for JSON in a backend system. Consider scalability, error handling, and production readiness.

Solution 
// JSON implementation
// Key aspects: validation, error handling, logging, testing

public class JSON {
    // Production-ready implementation
}
JSON Edge Cases

Identify and handle edge cases for JSON. What happens under high load, with invalid input, or during failures?

Solution 
// Edge case handling:
// 1. Null/empty input -> validation
// 2. High load -> rate limiting, queuing
// 3. Failures -> retries, circuit breaker
// 4. Concurrent access -> locks, idempotency
JSON Testing Strategy

Write a testing strategy for JSON. Include unit tests, integration tests, and performance tests.

Solution 
// Test plan:
// - Unit: 80% coverage target
// - Integration: API contracts
// - Performance: latency, throughput
// - Chaos: failure injection

Quiz

1. Which is the correct way to represent a string in JSON?

Question 1 options

2. What is the recommended date format for JSON APIs?

Question 2 options

3. What is a common mistake when implementing JSON?

Question 3 options

Flashcards

Question

What is JSON?

Click to reveal answer

Answer

JavaScript Object Notation — lightweight data interchange format

Question

JSON string rules?

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Answer

Must use double quotes — 'hello' is invalid, "hello" is valid

Question

JSON best practices

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Answer

Follow SOLID principles, write clean code, test thoroughly, document decisions, and monitor in production.

Revision Notes

Key Takeaways

  • 1. JSON is the standard format for API communication
  • 2. Strings require double quotes
  • 3. Use ISO 8601 for dates
  • 4. Always set Content-Type: application/json

Interview Tips

  • • Know JSON syntax rules
  • • Understand why JSON is preferred over XML

Cheat Sheet

JSON

  • Format: {"key": "value"}
  • Strings: Double quotes only
  • Dates: ISO 8601 (2026-08-15T10:30:00Z)
  • API: Always Content-Type: application/json
  • vs XML: JSON is lighter, easier to parse