Lazy Iterators

const result = Iter.fromArray([
  "apple",
  "banana",
  "cherry",
  "date",
  "elderberry",
])
  .enumerate()
  .map(([index, value]) => [index, value.toUpperCase()])
  .filter(([index, value]) => index % 2 === 0)
  .take(2)
  .intoArray();

This is now published under https://jsr.io/@hoodie/iterators.

Examples

Basic Usage

Create an iterator from an array and collect all elements into an array.

const array = [1, 2, 3, 4, 5];
const iterator = Iter.fromArray(array);
const result = iterator.intoArray();
console.log(result); // [1, 2, 3, 4, 5]

Enumerate

Create an iterator which yields the current index and the value of the original iterator.

const array = ["a", "b", "c"];
const iterator = Iter.fromArray(array).enumerate();
const result = iterator.intoArray();
console.log(result); // [[0, 'a'], [1, 'b'], [2, 'c']]

Filter

Create an iterator skipping all elements which don't meet the given predicate.

const array = [1, 2, 3, 4, 5];
const iterator = Iter.fromArray(array).filter((x) => x % 2 === 0);
const result = iterator.intoArray();
console.log(result); // [2, 4]

Find

Find the first element that satisfies the predicate.

const array = [1, 2, 3, 4, 5];
const iterator = Iter.fromArray(array);
const result = iterator.find((x) => x > 3);
console.log(result); // 4

Map

Create an iterator applying the given callback to each element.

const array = [1, 2, 3];
const iterator = Iter.fromArray(array).map((x) => x * 2);
const result = iterator.intoArray();
console.log(result); // [2, 4, 6]

Skip

Create an iterator skipping the first limit elements.

const array = [1, 2, 3, 4, 5];
const iterator = Iter.fromArray(array).skip(2);
const result = iterator.intoArray();
console.log(result); // [3, 4, 5]

Take

Create an iterator yielding the first limit elements.

const array = [1, 2, 3, 4, 5];
const iterator = Iter.fromArray(array).take(3);
const result = iterator.intoArray();
console.log(result); // [1, 2, 3]

Zip

Create an iterator that ‘Zips up’ two iterators into a single iterator of pairs.

const array1 = [1, 2, 3];
const array2 = ["a", "b", "c"];
const iterator1 = Iter.fromArray(array1);
const iterator2 = Iter.fromArray(array2);
const zipped = iterator1.zip(iterator2);
const result = zipped.intoArray();
console.log(result); // [[1, 'a'], [2, 'b'], [3, 'c']]

Cycle

Create an iterator that cycles through the elements of the original iterator.

const array = [1, 2, 3];
const iterator = Iter.fromArray(array).cycle();
const result = [];
for (let i = 0; i < 10; i++) {
  result.push(iterator.next().value);
}
console.log(result); // [1, 2, 3, 1, 2, 3, 1, 2, 3, 1]