Map string

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

• Use String.prototype.split() and Array.prototype.map() 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) =>
  str
    .split('')
    .map((c, i) => fn(c, i, str))
    .join('');

mapString('lorem ipsum', c => c.toUpperCase()); // 'LOREM IPSUM'