camelCase, snake_case, and kebab-case

Write three functions that convert text to a naming style: camelCase(text), snakeCase(text), and kebabCase(text). They accept text in any style, or a mix of styles, so each needs to find the words first.

A word is a run of letters and digits; letters include accented ones like é and û. Every other character (spaces, -, _, ., and so on) separates words, and several in a row count as one boundary.

Inside a run of letters and digits, a new word starts at an uppercase letter that follows a lowercase letter or a digit (backgroundColor, version2Beta), and at the last capital of a run of capitals that's followed by a lowercase letter (XMLHttpRequest is XML, Http, Request). A digit stays in the word it follows: html5 and top10 are single words.

camelCase writes the first word in lowercase and each later word with an uppercase first letter and the rest lowercase, with nothing between them. snakeCase writes every word in lowercase, joined with _, and kebabCase writes them in lowercase, joined with -. Text with no words gives "".

camelCase("background-color"); // "backgroundColor"
snakeCase("XMLHttpRequest");   // "xml_http_request"
kebabCase("FOO_BAR baz");      // "foo-bar-baz"
camelCase("version2 beta");    // "version2Beta"

What the tests check

1. 1converts space-separated words to each style

   expect(camelCase("hello big world")).toBe("helloBigWorld");
   expect(snakeCase("hello big world")).toBe("hello_big_world");
   expect(kebabCase("hello big world")).toBe("hello-big-world");
   

2. 2splits camelCase and PascalCase humps

   expect(kebabCase("backgroundColor")).toBe("background-color");
   expect(snakeCase("FirstName")).toBe("first_name");
   expect(camelCase("FirstName")).toBe("firstName");
   

3. 3treats any run of separators as one boundary

   expect(camelCase("--foo_bar  baz-")).toBe("fooBarBaz");
   expect(snakeCase("foo--bar__baz.qux")).toBe("foo_bar_baz_qux");
   expect(kebabCase(" foo / bar ")).toBe("foo-bar");
   

4. 4keeps a run of capitals together as one word

   expect(kebabCase("XMLHttpRequest")).toBe("xml-http-request");
   expect(snakeCase("userID")).toBe("user_id");
   expect(camelCase("parseHTMLString")).toBe("parseHtmlString");
   

5. 5lowercases words written in capitals

   expect(camelCase("FOO_BAR")).toBe("fooBar");
   expect(kebabCase("FOO BAR")).toBe("foo-bar");
   expect(camelCase("hello WORLD")).toBe("helloWorld");
   

6. 6keeps digits in the word they follow

   expect(kebabCase("version2Beta")).toBe("version2-beta");
   expect(snakeCase("html5 parser")).toBe("html5_parser");
   expect(camelCase("top 10 list")).toBe("top10List");
   

7. 7counts accented letters as letters

   expect(kebabCase("crèmeBrûlée")).toBe("crème-brûlée");
   expect(camelCase("crème brûlée")).toBe("crèmeBrûlée");
   expect(snakeCase("Ça Va")).toBe("ça_va");
   

8. 8returns an empty string when there are no words

   expect(camelCase("")).toBe("");
   expect(snakeCase("  --  ")).toBe("");
   expect(kebabCase("__")).toBe("");
   

Learn more

• String methodsLesson
• Character classes & setsLesson
• Unicode & string internalsLesson
• Write camelCase(text) and kebabCase(text) to convert between naming styles.Interview question