IterArray

IterArray is an iterable adapter that, given an iterable/generator or iterator, creates a new indexable lazy iterable that provides nth and slice methods.

Performance of IterArray instances are optimized for Array and primitive string iterables.

Usage.

const iterable = IterArray(new Set([5, 2, 8, 3, 4, 0, 9]))
 
iterable.nth(2) // 8
const slicedIterable = iterable.slice(1, 4) // IterArray([2, 8, 3])
slicedIterable.nth(2) // 3
;[...slicedIterable] // [2, 8, 3]
 
for (const x of iterable) {
    console.log(x) // log 5 2 8 3 4 0 9
}
 
for (const x of slicedIterable) {
    console.log(x) // log 2 8 3
}

API

constructor (iterable)

It creates a IterArray instance that iterates over the same values as iterable parameter or if iterable is a function, then it iterates over the same values as iterable(). It throws an exception if it is not passed an iterable, iterator or function that returns an iterable or an iterator.

Example:

const IterArray = require('iterarray')
 
function* gen () {
  yield 1
  yield 2
  yield 4
  yield 8
}
 
const iterableByArray = IterArray([1, 2, 3])
;[...iterableByArray] // [1, 2, 3]
const iterableBySet = IterArray(new Set([4, 5, 6]))
;[...iterableBySet] // [4, 5, 6]
const iterableByIterArray = IterArray(iterableByArray)
;[...iterableByIterArray] // [1, 2, 3]
const iterableByGenerator = IterArray(gen)
;[...iterableByGenerator] // [1, 2, 4, 8]
const iterableByIterator = IterArray(gen())
;[...iterableByIterator] // [1, 2, 4, 8]
const iterableByFunction = IterArray(() => iterableBySet)
;[...iterableByFunction] // [4, 5, 6]

nth (index)

It returns the index-th value that produces IterArray instance.

Internally, when .nth(index) is called, the values between 0 and index are cached. Then, if it is called nth with a lower index, no values are computed and if it is called with a greater index, only the values between index + 1 and the greater index are computed.

Example:

const IterArray = require('iterarray')
 
const iterable = IterArray([2, 5, 3, 7, 6, 1, 9, 4])
iterable.nth(2) // 3
iterable.nth(6) // 9
iterable.nth(0) // 2
iterable.nth(-5) // undefined
iterable.nth(10) // undefined
 

has (index)

It returns true if IterArray instance produces the index-th value.

Example:

const IterArray = require('iterarray')
 
const iterable = IterArray([2, 5, 3, 7, 6, 1, 9, 4])
iterable.has(0) // true
iterable.has(5) // true
iterable.nth(2) // true
iterable.nth(-5) // false
iterable.nth(21) // false
 

slice (start, end)

It returns an IterArray instance that iterates over the same values as sliced iterable.

Internally, the slice method does not slice the iterable, it just define a new iterable that iterates over sliced values (lazy evaluation). The sliced values of IterArray instance are also cached to get better performance when it called more than once.

length

A property of IterArray instance that can be an integer positive number or Infinity. The length property can be determined with a finite number only if all of the values of IterArray instance are cached.

In general, while not all of the values of iterable are traversed, length property is Infinity. However IterArray makes optimizations for arrays and primitive strings caching the values when the IterArray instance is created. Then, length is a finite number in a first instance.

Example:

const a = IterArray(new Set([1, 2]))
a.length // Infinity
a.nth(0) // 1
a.length // Infinity
a.nth(1) // 2
a.length // Infinity
a.nth(2) // undefined
a.length // 2
 
const b = IterArray(new Set([1, 2]))
b.length // Infinity
;[...b] // [1, 2]
b.length // 2
 
const c = IterArray([1, 2])
c.length // 2
 
const d = IterArray('abc')
c.length // 3

LICENSE

MIT