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Add iterator utility to prepend values to the beginning of an iterator
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‎lib/node_modules/@stdlib/iter/unshift/README.md‎

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<!--
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@license Apache-2.0
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Copyright (c) 2019 The Stdlib Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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-->
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# iterUnshift
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> Create an [iterator][mdn-iterator-protocol] which prepends values to the beginning of a provided [iterator][mdn-iterator-protocol].
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<!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. -->
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<section class="intro">
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</section>
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<!-- /.intro -->
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<!-- Package usage documentation. -->
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<section class="usage">
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## Usage
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```javascript
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var iterUnshift = require( '@stdlib/iter/unshift' );
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```
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#### iterUnshift( iterator, ...items )
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Returns an [iterator][mdn-iterator-protocol] which prepends values to the **beginning** of a provided [`iterator`][mdn-iterator-protocol].
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```javascript
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var array2iterator = require( '@stdlib/array/to-iterator' );
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var it = iterUnshift( array2iterator( [ 1, 2 ] ), 3, 4 );
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// returns <Object>
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var v = it.next().value;
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// returns 3
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v = it.next().value;
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// returns 4
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v = it.next().value;
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// returns 1
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v = it.next().value;
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// returns 2
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var bool = it.next().done;
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// returns true
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```
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The returned [iterator][mdn-iterator-protocol] protocol-compliant object has the following properties:
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- **next**: function which returns an [iterator][mdn-iterator-protocol] 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][mdn-iterator-protocol] is finished.
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- **return**: function which closes an [iterator][mdn-iterator-protocol] and returns a single (optional) argument in an [iterator][mdn-iterator-protocol] protocol-compliant object.
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</section>
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<!-- /.usage -->
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<!-- Package usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
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<section class="notes">
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## Notes
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- If an environment supports `Symbol.iterator` **and** a provided [iterator][mdn-iterator-protocol] is iterable, the returned [iterator][mdn-iterator-protocol] is iterable.
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</section>
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<!-- /.notes -->
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<!-- Package usage examples. -->
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<section class="examples">
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## Examples
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<!-- eslint no-undef: "error" -->
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```javascript
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var randu = require( '@stdlib/random/iter/randu' );
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var iterUnshift = require( '@stdlib/iter/unshift' );
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// Create a seeded iterator for generating pseudorandom numbers:
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var rand = randu({
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'seed': 1234,
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'iter': 10
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});
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// Create an iterator with prepended values:
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var it = iterUnshift( rand, 'beep', 'boop' );
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// Perform manual iteration...
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var v;
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while ( true ) {
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v = it.next();
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if ( v.done ) {
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break;
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}
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console.log( v.value );
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}
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```
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</section>
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<!-- /.examples -->
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<!-- Section to include cited references. If references are included, add a horizontal rule *before* the section. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
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<section class="references">
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</section>
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<!-- /.references -->
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<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
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<section class="links">
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[mdn-iterator-protocol]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterator_protocol
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</section>
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<!-- /.links -->

‎lib/node_modules/@stdlib/iter/unshift/benchmark/benchmark.js‎

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/**
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* @license Apache-2.0
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*
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* Copyright (c) 2019 The Stdlib Authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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'use strict';
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// MODULES //
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var bench = require( '@stdlib/bench' );
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var randu = require( '@stdlib/random/iter/randu' );
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var iterEmpty = require( '@stdlib/iter/empty' );
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var isnan = require( '@stdlib/math/base/assert/is-nan' );
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var isIteratorLike = require( '@stdlib/assert/is-iterator-like' );
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var pkg = require( './../package.json' ).name;
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var iterUnshift = require( './../lib' );
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// MAIN //
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bench( pkg, function benchmark( b ) {
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var iter;
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var it;
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var i;
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it = iterEmpty();
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b.tic();
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for ( i = 0; i < b.iterations; i++ ) {
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iter = iterUnshift( it, i );
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if ( typeof iter !== 'object' ) {
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b.fail( 'should return an object' );
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}
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}
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b.toc();
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if ( !isIteratorLike( iter ) ) {
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b.fail( 'should return an iterator protocol-compliant object' );
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}
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b.pass( 'benchmark finished' );
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b.end();
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});
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bench( pkg+'::iteration', function benchmark( b ) {
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var args;
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var iter;
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var it;
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var z;
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var i;
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it = randu({
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'iter': ( b.iterations > 100 ) ? b.iterations-100 : b.iterations
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});
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args = [ it ];
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for ( i = 0; i < 100; i++ ) {
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args.push( i );
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}
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iter = iterUnshift.apply( null, args );
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b.tic();
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for ( i = 0; i < b.iterations; i++ ) {
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z = iter.next().value;
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if ( isnan( z ) ) {
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b.fail( 'should not return NaN' );
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}
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}
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b.toc();
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if ( isnan( z ) ) {
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b.fail( 'should not return NaN' );
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}
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b.pass( 'benchmark finished' );
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b.end();
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});

‎lib/node_modules/@stdlib/iter/unshift/docs/repl.txt‎

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{{alias}}( iterator, ...items )
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Returns an iterator which prepends values to the beginning of a provided
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iterator.
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If an environment supports Symbol.iterator and a provided iterator is
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iterable, the returned iterator is iterable.
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Parameters
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----------
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iterator: Object
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Input iterator.
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items: ...any
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Items to prepend.
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Returns
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-------
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iterator: Object
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Iterator.
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iterator.next(): Function
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Returns an iterator protocol-compliant object containing the next
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iterated value (if one exists) and a boolean flag indicating whether the
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iterator is finished.
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iterator.return( [value] ): Function
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Finishes an iterator and returns a provided value.
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Examples
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--------
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> var it1 = {{alias:@stdlib/array/to-iterator}}( [ 1, 2 ] );
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> var it2 = {{alias}}( it1, 3, 4 );
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> var v = it2.next().value
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3
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> v = it2.next().value
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4
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> v = it2.next().value
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1
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> v = it2.next().value
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2
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> var bool = it2.next().done
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true
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See Also
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--------
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‎lib/node_modules/@stdlib/iter/unshift/examples/index.js‎

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/**
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* @license Apache-2.0
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*
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* Copyright (c) 2019 The Stdlib Authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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'use strict';
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var randu = require( '@stdlib/random/iter/randu' );
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var iterUnshift = require( './../lib' );
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var rand;
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var it;
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var v;
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// Create a seeded iterator for generating pseudorandom numbers:
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rand = randu({
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'seed': 1234,
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'iter': 10
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});
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// Create an iterator with prepended values:
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it = iterUnshift( rand, 'beep', 'boop' );
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// Perform manual iteration...
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while ( true ) {
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v = it.next();
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if ( v.done ) {
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break;
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}
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console.log( v.value );
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}

‎lib/node_modules/@stdlib/iter/unshift/lib/index.js‎

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/**
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* @license Apache-2.0
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*
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* Copyright (c) 2019 The Stdlib Authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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'use strict';
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/**
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* Create an iterator which prepends values to the beginning of a provided iterator.
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*
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* @module @stdlib/iter/unshift
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*
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* @example
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* var array2iterator = require( '@stdlib/array/to-iterator' );
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* var iterUnshift = require( '@stdlib/iter/unshift' );
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*
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* var iter = iterUnshift( array2iterator( [ 1, 2 ] ), 3, 4 );
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*
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* var v = iter.next().value;
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* // returns 3
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*
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* v = iter.next().value;
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* // returns 4
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*
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* v = iter.next().value;
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* // returns 1
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*
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* v = iter.next().value;
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* // returns 2
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*
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* var bool = iter.next().done;
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* // returns true
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*/
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// MODULES //
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var iterUnshift = require( './main.js' );
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// EXPORTS //
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module.exports = iterUnshift;

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