Group duplicate prefixes in the strings: (src: string[]) => string[]

groupByPrefix.ts

const getInitials = (src: string[], length = 1) =>
  Array.from(new Set(src.map(v => v.substring(0, length))));

export default (src: string[]) =>
  getInitials(src).map(initial => {
    const list = src.filter(v => v.match(`^${initial}`));
    const rec = (prev: string, length = 2): string => {
      const [word, ...{ length: l }] = getInitials(list, length);

      return l || list[0].length < length ? prev : rec(word, length + 1);
    };

    return rec(initial);
  });