camelCase Converter
camelCase writes helloWorldExample. It is the convention for variables and methods in JavaScript, TypeScript, Java, Swift and Kotlin — the first word lowercase, every subsequent word capitalised, no separators.
Conversions
| Input | camelCase |
|---|---|
hello world example | helloWorldExample |
XMLHttpRequest | xmlHttpRequest |
user_first_name | userFirstName |
Total Order Count | totalOrderCount |
XMLHttpRequest splits into XML, Http, Request, so camelCase gives xmlHttpRequest — the leading acronym lower-cases entirely while the inner one keeps its shape. Naive converters produce xMLHttpRequest, which is what the browser API is actually called and is widely considered a mistake in the original spec.The Same Text in Other Cases
| Case | Result |
|---|---|
| PascalCase | HelloWorldExample |
| snake_case | hello_world_example |
| SCREAMING_SNAKE_CASE | HELLO_WORLD_EXAMPLE |
| kebab-case | hello-world-example |
| Train-Case | Hello-World-Example |
| dot.case | hello.world.example |
Where camelCase Fits
camelCase is the default for values in the C-family languages that took it from Java: variables, function names, object properties and method names. Its distinguishing feature is that the first character stays lowercase, which is what separates it from PascalCase and, in several languages, what separates a value from a type.
Converting in Code
``javascript
const camel = (s) =>
words(s)
.map((w, i) => (i === 0 ? w.toLowerCase() : w[0].toUpperCase() + w.slice(1).toLowerCase()))
.join('');
`
The first word is the special case. Every implementation that forgets it produces TotalCount instead of totalCount, which in Go would export the identifier and in JSON would break a field name consumers already depend on.
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
``