JavaScript Object Notation (JSON) is a lightweight, text-based, language-independent data interchange format. It is derived from the JavaScript programming language but is now widely supported by all major programming languages (e.g., Python, Java, C++, Go). JSON is designed for easy reading and writing by humans, as well as efficient parsing and generation by machines. It is the de facto standard for data transmission in web APIs, client-server communication, and configuration file storage.
Core Syntax Rules
JSON data is structured using two fundamental data structures:
- Objects
- Enclosed in curly braces
{}. - Consist of key-value pairs, where keys must be double-quoted strings.
- Values are separated from keys by a colon
:, and key-value pairs are separated by commas,. - Example:json
{ "deviceId": "DHCP-2025-001", "ipAddress": "192.168.1.105", "leaseDuration": 86400, "isConnected": true, "dnsServers": ["8.8.8.8", "8.8.4.4"] }
- Enclosed in curly braces
- Arrays
- Enclosed in square brackets
[]. - Contain an ordered list of values (strings, numbers, booleans, objects, other arrays, or
null). - Values are separated by commas
,. - Example:json
[ {"protocol": "HTTP", "port": 80}, {"protocol": "HTTPS", "port": 443}, {"protocol": "DHCP", "port": 67} ]
- Enclosed in square brackets
Valid Value Types
JSON only supports the following data types for values:
- String: Double-quoted Unicode characters (e.g.,
"proxyServer"). - Number: Integer or floating-point (e.g.,
67,1.23; no hexadecimal or octal notation). - Boolean:
trueorfalse(lowercase only). - Null:
null(represents an empty value; lowercase only). - Object: Nested JSON object (e.g.,
{"network": {"type": "LAN"}}). - Array: Nested JSON array (e.g.,
["TCP", "UDP"]).
Syntax Restrictions
- No comments are allowed in standard JSON.
- Trailing commas after the last key-value pair or array element are prohibited.
- Single quotes are not permitted for keys or strings.
Key Advantages
- Lightweight: More compact than XML (no closing tags), reducing data transmission size and latency.
- Human-readable: Simple and intuitive syntax, easier to debug than binary formats (e.g., Protocol Buffers).
- Language-agnostic: Supported by all mainstream programming languages with built-in or third-party libraries.
- Fast Parsing: Most programming languages provide high-performance JSON parsers for efficient data processing.
Common Use Cases
- Web API Communication: Used to exchange data between frontend applications (e.g., React, Vue) and backend servers.
- Configuration Files: Replaces XML or INI files for application settings (e.g.,
package.jsonin Node.js projects). - Data Storage: Stores structured data in databases or flat files for small-scale applications.
- IoT Device Data Transmission: Transmits lightweight sensor data between IoT devices and cloud platforms.
Difference Between JSON and JavaScript Objects
| Feature | JSON | JavaScript Object |
|---|---|---|
| Key Requirement | Keys must be double-quoted strings | Keys can be unquoted or single-quoted |
| Value Types | Supports 6 standard types | Supports additional types (e.g., functions, dates, undefined) |
| Comments | Not allowed | Allowed (// or /* */) |
| Trailing Commas | Prohibited | Allowed in modern JavaScript |
| Purpose | Data interchange format | Code construct for programming |
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