[answer - typescript/camelCase]

[tyankatsu0105]

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const regex = /([A-Z]|[a-z]|[0-9])+/g;

export const camelCase = (str: string) => {
  const matched = str.match(regex);
  if (matched === null) return "";

  let [first, ...rest] = matched;
  first = first.toLocaleLowerCase();
  rest = rest.map(letter => {
    const lowerLetter = letter.toLocaleLowerCase();
    let [first, ...rest] = lowerLetter;

    return `${first.toLocaleUpperCase()}${rest.join("")}`;
  });

  return `${first}${rest.join("")}`;
};