Constant Case Converter
SCREAMING_SNAKE_CASE writes HELLO_WORLD_EXAMPLE. Constant case is the near-universal convention for environment variables and compile-time constants: DATABASE_URL, MAX_RETRY_COUNT, HTTP_TIMEOUT_MS. Shells, Docker, Kubernetes and every twelve-factor deployment tool expect it, and POSIX reserves all-caps names for the environment specifically so they cannot collide with shell variables.
Conversions
| Input | SCREAMING_SNAKE_CASE |
|---|---|
hello world example | HELLO_WORLD_EXAMPLE |
XMLHttpRequest | XML_HTTP_REQUEST |
user_first_name | USER_FIRST_NAME |
Total Order Count | TOTAL_ORDER_COUNT |
XMLHttpRequest becomes XML_HTTP_REQUEST. The conversion is lossy in one direction — DB_URL could have come from dbUrl or DBUrl, and nothing in the output says which.The Same Text in Other Cases
| Case | Result |
|---|---|
| camelCase | helloWorldExample |
| PascalCase | HelloWorldExample |
| snake_case | hello_world_example |
| kebab-case | hello-world-example |
| Train-Case | Hello-World-Example |
| dot.case | hello.world.example |
What Actually Belongs in a Constant
A constant is a value fixed at compile time and meaningful by name rather than by number — MAX_RETRY_COUNT, DEFAULT_TIMEOUT_MS, HTTP_PORT. Naming it removes the magic number and gives the reason for the value somewhere to live.
The convention is near-universal, which is why it carries safely across a codebase mixing several languages. Where it breaks down is in languages treating capitalisation as semantics: in Ruby every capitalised identifier is a constant, and in Go a capitalised one is exported.
Converting in Code
``javascript
const constant = (s) => words(s).map((w) => w.toUpperCase()).join('_');
`
POSIX permits only letters, digits and underscore in an environment variable name, and forbids a leading digit. A converter that faithfully preserves a hyphen produces a name the shell silently ignores rather than rejects.
Converting at the API Boundary
The recurring friction is that JavaScript uses camelCase and Python, Ruby, Go and SQL use
snake_case. The fix is to convert in exactly one place — the client that talks to the API —
rather than letting both conventions into the same codebase.
`javascript
const toCamel = (s) => s.replace(/_([a-z])/g, (_, c) => c.toUpperCase());
const toSnake = (s) => s.replace(/[A-Z]/g, (c) => '_' + c.toLowerCase());
// Recursively, for a whole payload
const convertKeys = (value, fn) =>
Array.isArray(value)
? value.map((v) => convertKeys(v, fn))
: value && typeof value === 'object'
? Object.fromEntries(Object.entries(value).map(([k, v]) => [fn(k), convertKeys(v, fn)]))
: value;
`
Two things to watch: keys that are user data rather than field names must not be
converted, and the round trip is not always lossless — userID → user_id → userId
changes the original.
Where Each Convention Is Mandatory
Not stylistic — these will break if you deviate:
| Context | Requirement |
|---|---|
| Environment variables | Uppercase with underscores; POSIX reserves lowercase |
| Custom HTML elements | Must contain a hyphen |
| Python modules | Cannot contain hyphens; the import statement will not parse |
| SQL identifiers | Folded to one case unless quoted, so camelCase does not survive |
| React components | Must start uppercase, or JSX treats it as an HTML tag |
Renaming Safely
A find-and-replace across a codebase will hit strings, comments and unrelated identifiers.
Use your language server's rename symbol instead — it understands scope. For a bulk rename
across files, restrict the pattern with word boundaries and review the diff before
committing:
`bash
grep -rn '\buserId\b' src/ # look first
``