30-seconds-of-code/snippets/join.md

join

Joins all elements of an array into a string and returns this string. Uses a separator and an end separator.

Use Array.reduce() to combine elements into a string. Omit the second argument, separator, to use a default separator of ','. Omit the third argument, end, to use the same value as separator by default.

const join = (arr, separator = ',', end = separator) =>
  arr.reduce(
    (acc, val, i) =>
      i == arr.length - 2
        ? acc + val + end
        : i == arr.length - 1 ? acc + val : acc + val + separator,
    ''
  );

join(); // ''
join(['pen','pineapple','apple','pen'],',','&'); //"pen,pineapple,apple&pen"
join(['pen','pineapple','apple','pen'],','); //"pen,pineapple,apple,pen"
join(['pen','pineapple','apple','pen']); //"pen,pineapple,apple,pen"