A TypeScript utility function for converting between different casing conventions.

convert-to-casing.ts

/**
 * A union of the possible casing formats.
 */
export type CasingFormat =
	| "lower case"
	| "UPPER CASE"
	| "Title Case"
	| "camelCase"
	| "PascalCase"
	| "snake_case"
	| "SCREAMING_SNAKE_CASE"
	| "camel_Snake_Case"
	| "Pascal_Snake_Case";

/**
 * A regular expression used to split a string into words.
 */
const TO_WORDS_REGEX: RegExp = /\S+?(?=\s|[A-Z]|$)/gu;

/**
 * Returns an array of words from a string.
 * 
 * @param words {string} The string to split into words.
 * @return {string[]} An array of words extracted from the string.
 */
const toWords = (words: string): string[] => words.match(TO_WORDS_REGEX) ?? [];

/**
 * Returns the lower case version of a string.
 * 
 * @param word {string} The string to convert to lower case.
 * @return {string} The lower case version of the string.
 */
const toLowerCase = (word: string): string => word.toLowerCase();

/**
 * Returns the upper case version of a string.
 * 
 * @param word {string} The string to convert to upper case.
 * @return {string} The upper case version of the string.
 */
const toUpperCase = (word: string): string => word.toUpperCase();

/**
 * Returns the title case version of a string.
 * 
 * @param word {string} The string to convert to title case.
 * @return {string} The title case version of the string.
 */
const toTitleCase = (word: string): string => {
	const letters: string[] = word.split("");
	return letters.slice(0, 1).map(toUpperCase).join("") +
		letters.slice(1).map(toLowerCase).join("");
};

/**
 * Returns a modified version of the input string array, having removed all
 * non-alphanumeric characters from each string.
 * 
 * @param words {string[]} The strings to process.
 * @return {string[]} An array of string with non-alphanumeric characters
 * removed.
 */
const stripNonAlphaNumeric = (...words: string[]): string[] =>
	words.map((word: string) => word.replace(/[^a-zA-Z0-9]/g, ""));

/**
 * A mapping of casing formats to their respective formatting functions.
 */
const CASING_FORMATTERS: Record<CasingFormat, (words: string[]) => string> = {
	"lower case": (words: string[]): string => words.map(toLowerCase).join(" "),
	"UPPER CASE": (words: string[]): string => words.map(toUpperCase).join(" "),
	"Title Case": (words: string[]): string => words.map(toTitleCase).join(" "),
	"camelCase": (words: string[]): string => [
		...stripNonAlphaNumeric(...words).slice(0, 1).map(toLowerCase),
		...stripNonAlphaNumeric(...words).slice(1).map(toTitleCase)
	].join(""),
	"PascalCase": (words: string[]): string =>
		stripNonAlphaNumeric(...words).map(toTitleCase).join(""),
	"snake_case": (words: string[]): string =>
		stripNonAlphaNumeric(...words).map(toLowerCase).join("_"),
	"SCREAMING_SNAKE_CASE": (words: string[]): string =>
		stripNonAlphaNumeric(...words).map(toUpperCase).join("_"),
	"camel_Snake_Case": (words: string[]): string => [
		...stripNonAlphaNumeric(...words).slice(0, 1).map(toLowerCase),
		...stripNonAlphaNumeric(...words).slice(1).map(toTitleCase)
	].join("_"),
	"Pascal_Snake_Case": (words: string[]): string =>
		stripNonAlphaNumeric(...words).map(toTitleCase).join("_"),
};

/**
 * Converts a string to the specified casing format.
 * 
 * @param input {string} The string to convert.
 * @param casing {CasingFormat} The casing format to convert the string to.
 * @return {string} The converted string in the specified casing format.
 */
export const convertToCasing = (input: string, casing: CasingFormat): string =>
	CASING_FORMATTERS[casing](toWords(input));