How to name variables, functions, classes, constants, files.

• variables & functions: camelCase → userName, getUserById
• classes & constructors: PascalCase → UserService, HttpClient
• true constants: UPPER_SNAKE_CASE → MAX_RETRIES, API_URL
• private-ish: leading underscore → _internalCache
• files: kebab-case → user-service.js
• booleans read as yes/no: isActive, hasPermission, canEdit
• identifiers can't start with a digit; can't be reserved words (class, return...)

See examples/.

Rename 5 poorly-named variables in a sample file.