Create an iterator which returns the union of two or more iterators.

Usage no npm install needed!

<script type="module">
  import stdlibIterUnion from 'https://cdn.skypack.dev/@stdlib/iter-union';



NPM version Build Status Coverage Status

Create an iterator which returns the union of two or more iterators.


npm install @stdlib/iter-union


var iterUnion = require( '@stdlib/iter-union' );

iterUnion( iter0, ...iterator )

Returns an iterator which returns the union of two or more iterators.

var array2iterator = require( '@stdlib/array-to-iterator' );

var it1 = array2iterator( [ 2, 1, 1, 2, 4 ] );
var it2 = array2iterator( [ 3, 4, 3 ] );

var it = iterUnion( it1, it2 );
// returns <Object>

var v = it.next().value;
// returns 2

v = it.next().value;
// returns 1

v = it.next().value;
// returns 4

v = it.next().value;
// returns 3

var bool = it.next().done;
// returns true

The returned iterator protocol-compliant object has the following properties:

  • next: function which returns an iterator protocol-compliant object containing the next iterated value (if one exists) assigned to a value property and a done property having a boolean value indicating whether the iterator is finished.
  • return: function which closes an iterator and returns a single (optional) argument in an iterator protocol-compliant object.


  • Value "uniqueness" is determined according to strict equality.
  • A returned iterator internally buffers unique values and, thus, has O(N) memory requirements, where N is the total number of iterator source values.
  • If an environment supports Symbol.iterator and all provided iterators are iterable, the returned iterator is iterable.


var discreteUniform = require( '@stdlib/random-iter-discrete-uniform' );
var iterUnion = require( '@stdlib/iter-union' );

// Create seeded iterators which can generate 1000 pseudorandom numbers:
var rand1 = discreteUniform( 1, 10, {
    'seed': 1234,
    'iter': 1000
var rand2 = discreteUniform( 6, 15, {
    'seed': 1234,
    'iter': 1000

// Create an iterator which returns the union of the seeded iterators:
var it = iterUnion( rand1, rand2 );

// Perform manual iteration...
var v;
while ( true ) {
    v = it.next();
    if ( v.done ) {
    console.log( v.value );


This package is part of stdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.






Copyright © 2016-2022. The Stdlib Authors.