BEM Class Name Converter
kebab-case writes hello-world-example. BEM writes block__element--modifier, with each of the three parts in kebab-case: card__title--featured. The point is a flat, specificity-free namespace — every selector is one class, so nothing wins by nesting and the cascade never surprises you. That predictability is why BEM survived the arrival of CSS modules and utility frameworks.
Conversions
| Input | kebab-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. That is the correct behaviour for a URL or a CSS class, where case sensitivity varies by context and mixed case causes more problems than it solves.The Same Text in Other Cases
| Case | Result |
|---|---|
| camelCase | helloWorldExample |
| PascalCase | HelloWorldExample |
| snake_case | hello_world_example |
| SCREAMING_SNAKE_CASE | HELLO_WORLD_EXAMPLE |
| Train-Case | Hello-World-Example |
| dot.case | hello.world.example |
Why BEM Uses Three Parts
block__element--modifier encodes the relationship in the name, so the stylesheet never needs a descendant selector. Every rule is a single class, specificity stays flat, and nothing wins by being nested more deeply — which is what makes a large BEM stylesheet predictable to change.
The double underscore and double hyphen exist to be visually distinct from the single hyphens inside each part, so card__nav-item--is-active parses unambiguously by eye.
Converting in Code
``javascript
const kebab = (s) => words(s).map((w) => w.toLowerCase()).join('-');
`
A hyphen is a subtraction operator in most languages, so kebab-case identifiers cannot be used unquoted in code. That is precisely why it belongs in URLs, CSS and filenames and not in variable names.
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
``