Iterator.prototype.join()

The join() method of {{jsxref("Iterator")}} instances is similar to {{jsxref("Array.prototype.join()")}}: it returns a string that is the concatenation of all elements produced by the iterator, separated by commas or a specified separator string. If the iterator has only one item, that item's stringification is returned without using the separator.

Syntax#

join()
join(separator)

Parameters#

• separator {{optional_inline}}
• : A string to separate each pair of adjacent elements of the iterator. If omitted, the elements are separated with a comma (",").

Return value#

A string joining all yielded elements. The elements are converted to strings. If an element is undefined or null, it is converted to an empty string instead of the string "null" or "undefined". If the iterator is empty, the empty string is returned.

Description#

See {{jsxref("Array.prototype.join()")}} for details about how join() works. Unlike most other iterator helper methods, it does not work well with infinite iterators, because it is not lazy.

Examples#

Using join()#

function* fibonacci() {
  let current = 1;
  let next = 1;
  while (true) {
    yield current;
    [current, next] = [next, current + next];
  }
}

console.log(fibonacci().take(5).join()); // "1,1,2,3,5"
console.log(fibonacci().take(5).join(" - ")); // "1 - 1 - 2 - 3 - 5"

Specifications#

{{Specifications}}

Browser compatibility#

{{Compat}}

See also#

• Polyfill of Iterator.prototype.join in core-js
• es-shims polyfill of Iterator.prototype.join
• {{jsxref("Iterator")}}
• {{jsxref("Iterator.prototype.reduce()")}}
• {{jsxref("Array.prototype.join()")}}