Creates a new string with the results of calling a provided function on every character in the given string.

  • Use String.prototype.split('') and to call the provided function, fn, for each character in str.
  • Use Array.prototype.join('') to recombine the array of characters into a string.
  • The callback function, fn, takes three arguments (the current character, the index of the current character and the string mapString was called upon).
const mapString = (str, fn) =>
    .map((c, i) => fn(c, i, str))
mapString('lorem ipsum', c => c.toUpperCase()); // 'LOREM IPSUM'