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:bulb: Differences and usage criteria for the common case styles used when naming variables, functions, files, and URLs in programming.

[01] Case Styles at a Glance

Style Example Rule Aliases
camelCase getUserName First word lowercase, subsequent words capitalized lower camelCase
PascalCase GetUserName Every word capitalized upper camelCase
snake_case get_user_name All lowercase, words joined by underscore _  
SCREAMING_SNAKE_CASE GET_USER_NAME All uppercase, words joined by underscore _ UPPER_SNAKE_CASE
kebab-case get-user-name All lowercase, words joined by hyphen - dash-case, lisp-case

Same meaning, five ways:



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camelCase:              myVariableName
PascalCase:             MyVariableName
snake_case:             my_variable_name
SCREAMING_SNAKE_CASE:   MY_VARIABLE_NAME
kebab-case:             my-variable-name

[02] Each Style In Detail

2-1. camelCase

First word lowercase, subsequent words capitalized at the first letter. The “humps” resemble a camel’s, hence camelCase.



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// JavaScript — variables, functions
let userName = "admin";
function getUserProfile() { ... }
const maxRetryCount = 3;

Main uses:

  • JavaScript / TypeScript — variables, functions
  • Java — variables, methods
  • Swift, Kotlin — variables, functions

2-2. PascalCase

Every word capitalized at the first letter. A variant of camelCase, originating from Pascal.



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# Python — classes
class UserProfile:
    pass

class HttpRequestHandler:
    pass





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// TypeScript — classes, interfaces, types
class UserService { ... }
interface ApiResponse { ... }
type UserRole = "admin" | "user";

Main uses:

  • Almost every language — class names
  • TypeScript — interfaces, types
  • React — component names
  • C# — methods, properties

2-3. snake_case

All lowercase, joined by underscore _.



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# Python — variables, functions
user_name = "admin"
def get_user_profile():
    pass
max_retry_count = 3





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# Ruby — variables, methods
user_name = "admin"
def get_user_profile
end

Main uses:

  • Python — variables, functions, modules
  • Ruby — variables, methods
  • Rust — variables, functions
  • SQL — tables, columns
  • C — variables, functions

2-4. SCREAMING_SNAKE_CASE

All uppercase, joined by underscore. As the name “screaming snake” suggests, used for constants.



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# Python — constants
MAX_RETRY_COUNT = 3
DATABASE_URL = "postgresql://localhost/mydb"
DEFAULT_TIMEOUT_SECONDS = 30





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// Java — constants
public static final int MAX_RETRY_COUNT = 3;
public static final String API_BASE_URL = "https://api.example.com";

Main uses:

  • Almost every language — constants
  • Environment variables — DATABASE_URL, API_KEY

2-5. kebab-case

All lowercase, joined by hyphen -. The hyphens pierce words like a kebab skewer, hence kebab-case.



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<!-- HTML — attributes, CSS classes -->
<div class="user-profile" data-user-id="123">
  <span class="user-name">admin</span>
</div>





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/* CSS — properties, classes */
.user-profile {
  font-size: 14px;
  background-color: #fff;
  max-width: 1200px;
}





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# URL path
https://example.com/api/user-profile
https://example.com/blog/my-first-post

Main uses:

  • HTML — attributes, custom tags
  • CSS — class names, properties
  • URL — paths
  • File names — user-profile.js, api-handler.ts
  • CLI options — --max-retry, --output-dir

:warning: kebab-case cannot be used as a variable name in most programming languages — hyphen - is interpreted as the subtraction operator.



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// X impossible — interpreted as subtraction
let user-name = "admin";  // SyntaxError

// O variables use camelCase
let userName = "admin";

[03] Language-Specific Conventions

Language/Env Variables/Functions Classes/Types Constants File names
JavaScript camelCase PascalCase SCREAMING_SNAKE kebab-case
TypeScript camelCase PascalCase SCREAMING_SNAKE kebab-case
Python snake_case PascalCase SCREAMING_SNAKE snake_case
Java camelCase PascalCase SCREAMING_SNAKE PascalCase
Go camelCase PascalCase PascalCase snake_case
Rust snake_case PascalCase SCREAMING_SNAKE snake_case
Ruby snake_case PascalCase SCREAMING_SNAKE snake_case
C / C++ snake_case PascalCase SCREAMING_SNAKE snake_case
C# camelCase PascalCase PascalCase PascalCase
Swift camelCase PascalCase camelCase PascalCase
Kotlin camelCase PascalCase SCREAMING_SNAKE PascalCase
SQL snake_case - - snake_case
HTML/CSS kebab-case - - kebab-case
URL kebab-case - - -
Env variables - - SCREAMING_SNAKE -

:bulb: Within a single project, the case style varies by target. In JavaScript: variables camelCase, classes PascalCase, constants SCREAMING_SNAKE_CASE, file names kebab-case.

[04] Real Example — One Project Using Multiple Styles

A React + TypeScript project uses 4 styles in one project:



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src/
├── components/
│   └── user-profile/              ← directory: kebab-case
│       ├── UserProfile.tsx        ← component file: PascalCase
│       └── user-profile.css       ← style file: kebab-case
├── utils/
│   └── api-handler.ts             ← util file: kebab-case
└── constants/
    └── config.ts





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// config.ts
export const API_BASE_URL = "https://api.example.com";   // constant: SCREAMING_SNAKE
export const MAX_RETRY_COUNT = 3;

// UserProfile.tsx
import React from 'react';

interface UserProfileProps {    // interface: PascalCase
  userName: string;            // property: camelCase
  isActive: boolean;
}

class UserService {            // class: PascalCase
  getUserById(userId: number) {  // method, parameter: camelCase
    const requestUrl = `${API_BASE_URL}/users/${userId}`;
    return fetch(requestUrl);
  }
}





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/* user-profile.css */
.user-profile {               /* class: kebab-case */
  max-width: 600px;           /* CSS property: kebab-case */
  background-color: #f5f5f5;
}

.user-profile__header {       /* BEM notation also kebab-based */
  font-size: 18px;
}

[05] Selection Criteria

5-1. Default Rule



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Follow the language/framework's official style guide.
Where to look Examples
Python PEP 8
JavaScript Airbnb Style Guide, Google Style Guide
Go Effective Go
Rust Rust API Guidelines
Java Google Java Style Guide

5-2. When No Official Guide

Context Recommendation
URL, file names kebab-case (SEO, readability)
Env variables SCREAMING_SNAKE_CASE
DB tables/columns snake_case
API JSON fields camelCase (frontend) or snake_case (backend)
Config file keys kebab-case (YAML, CLI) or camelCase (JSON)

5-3. Most Important

:bulb: Whatever style you pick, consistency within a project matters most. Mixing userName and user_name for the same thing causes confusion.

[06] Summary

Style Form Typical use
camelCase myVariable JS/Java variables, functions
PascalCase MyClass classes, components, types
snake_case my_variable Python/Rust/Ruby variables, DB
SCREAMING_SNAKE MY_CONSTANT constants, env variables
kebab-case my-component URL, CSS, HTML, file names 


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Naming rule = language convention + target type + project consistency

참고