JSON Objects

Learning Focus

Objects are the most fundamental JSON container. Every real-world API payload is an object or an array of objects. Master the rules and patterns here.

What is a JSON Object?

An object is an unordered collection of zero or more key-value pairs wrapped in {}.

{
  "id":        1001,
  "username":  "alice",
  "email":     "alice@example.com",
  "createdAt": "2024-01-15T08:30:00Z",
  "isActive":  true,
  "metadata":  null
}

Rules

1. Keys must be double-quoted strings
2. Key-value pairs separated by ,
3. Key and value separated by :
4. No trailing comma after the last pair
5. Order is not guaranteed — parsers may reorder keys
6. Avoid duplicate keys — parser behaviour is undefined

Nested Objects

{
  "user": {
    "id": 123,
    "profile": {
      "firstName": "Alice",
      "address": {
        "city": "Singapore",
        "postal": "018989"
      }
    }
  }
}

Language Mappings

Language	JSON Object Maps To
JavaScript	{} object literal
Python	dict
Go	struct (typed) or map[string]interface{}
PHP	stdClass or associative array
Ruby	Hash

Concept Map

Concept Flow

JSON Object  →  Unordered Key-Value Pairs
                  ├── Keys: double-quoted strings
                  └── Values: any JSON type
                              └── Nesting allowed
                                    └── Real-world API payloads

Common Pitfalls

Pitfall	Consequence	Prevention
Duplicate keys	Parser-dependent behaviour	Ensure unique keys
Assuming key order	Breaks order-sensitive logic	Use arrays if order matters
Missing comma between pairs	Parse error	Use a linter or formatter
Trailing comma	Parse error	Remove or use JSONC parser

What's Next

• Previous: Booleans and Null — Review literal types.
• Next: JSON Arrays — Learn the ordered list container.
• Section Overview — Return to the Data Types module index.