underscoretocamelcase

underscoretocamelcase refers to converting a string written with underscores as word separators (snake_case) into a camelCase form. The most common target is lowerCamelCase, where the first word is lowercase and each subsequent word starts with an uppercase letter, with all words concatenated. This transformation is frequently used when adapting identifiers between languages and coding styles.

Two common variants are lowerCamelCase and UpperCamelCase (also called PascalCase). For example, 'hello_world' becomes 'helloWorld' in lowerCamelCase and 'HelloWorld' in UpperCamelCase. Some contexts preserve acronyms differently, producing 'HTTPServerError' or 'httpServerError' depending on the library.

Algorithmically, the transformation splits the input on underscores, discards empty tokens caused by consecutive or leading/trailing underscores, lowercases the first token, capitalizes the first letter of each remaining token, and concatenates the tokens. Implementations differ on how to handle consecutive underscores and existing capitalization in the input.

In practice, underscoretocamelcase appears in code generation, data serialization, and API adapters. It is supported by many languages and libraries: JavaScript libraries such as lodash.camelCase, Python utilities with regular expressions or builtin string methods, Java's Guava CaseFormat, and Ruby on Rails' String#camelize. Some tools let you choose whether to preserve acronyms as uppercase or to lowercase them first.

Common pitfalls include handling acronyms, leading underscores, or strings that contain non-letter characters. The resulting name may also diverge across platforms, so it is important to apply consistent rules within a project. Related concepts include snake_case, camelCase, PascalCase, and kebab-case.