Capitalize first names derived from an email address (Dutch)

capitalize.ts

export const capitalize = (s: string) => s.charAt(0).toUpperCase() + s.slice(1);

/** Capitalize first names that are derived from an email, like anne_merel or jan_willem. */
export const capitalizeName = (s: string) =>
  /^ij/i.test(s) // names like IJsbrand
    ? s.replace(/^ij/i, 'IJ')
    : /_/.test(s) // names like jan_willem
    ? s.split('_').map(capitalize).join('-')
    : capitalize(s); // other names