lazy-iterable

LazyIterable

An iterable object that lazily implements many Array.prototype members.

function * generator () {
  yield 1
  yield 2
  yield 3
}

const lazy = new LazyIterable(generator)

const array = lazy.map(v => v * 2).toArray()

console.log(array) // [2, 4, 6]

The advantage that LazyIterable has over Array is that the its source is evaluated as late as possible.

let iterated = false

function * generator () {
  iterated = true
  yield 1
  yield 2
  yield 3
}

let lazy = new LazyIterable(generator)
console.log(iterated) // false

lazy = lazy.map(v => v * 2)
console.log(iterated) // false

const array = lazy.toArray()
console.log(iterated) // true

LazyIterable implements most of the read-only members of Array.prototype as well as a couple in-place members in a read-only fashion.

• Lazy members
  • concat
  • entries
  • filter
  • keys
  • map
  • reverse
  • slice
  • sort
  • values
• Eager members:
  • length
  • every
  • find
  • findIndex
  • forEach
  • includes
  • indexOf
  • itemAt
  • join
  • reduce
  • reduceRight
  • some
  • toArray

reverse and sort each return a new LazyIterable whereas Array performs the action in-place.

Read more in the API Documentation.