joinAndWrap = (arr, left, right, separator = ' ') =>
  left + arr.join(right + separator + left) + right
Joins all elements of an array into a string where all elements
are wrapped between `left` and `right`.

@param {Array} arr - The array to perform the join on.
@param {string} left - The wrapping string for the left side.
@param {string} right - The wrapping string for the right side.
@param {string} [separator] - The separator between a wrapped element
    and the next one. Defaults to space.
@return {string} The wrapped string, e.g. `[[hello]] [[world]]`.