What is camelCase?

camelCase is a naming convention where multi-word identifiers are written without spaces or punctuation, with each word after the first capitalized. For example, "user first name" becomes "userFirstName". It is called camelCase because the capital letters in the middle of the compound word resemble the humps of a camel.

Where is camelCase used?

camelCase is the standard naming convention for variables and functions in JavaScript, TypeScript, Java, and Swift. It is also used for JSON property names, CSS-in-JS properties, and React component props. Most JavaScript style guides (including Airbnb and Google) mandate camelCase for local variables and function names.

// JavaScript — convert string to camelCase
function toCamelCase(str) {
  return str
    .replace(/[-_\s]+(.)?/g, (_, c) => (c ? c.toUpperCase() : ''));
}
toCamelCase('user_first_name');  // 'userFirstName'
toCamelCase('hello-world');       // 'helloWorld'

# Python — convert string to camelCase
def to_camel_case(s):
    parts = s.replace('-', '_').split('_')
    return parts[0].lower() + ''.join(w.capitalize() for w in parts[1:])
to_camel_case('user_first_name')  # 'userFirstName'