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iterUnshift

Create an iterator which prepends values to the beginning of a provided iterator.

Installation

npm install @stdlib/iter-unshift

Alternatively,

• To load the package in a website via a script tag without installation and bundlers, use the ES Module available on the esm branch (see README).
• If you are using Deno, visit the deno branch (see README for usage intructions).
• For use in Observable, or in browser/node environments, use the Universal Module Definition (UMD) build available on the umd branch (see README).

The branches.md file summarizes the available branches and displays a diagram illustrating their relationships.

To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.

Usage

var iterUnshift = require( '@stdlib/iter-unshift' );

iterUnshift( iterator, ...items )

Returns an iterator which prepends values to the beginning of a provided iterator.

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

var it = iterUnshift( array2iterator( [ 1, 2 ] ), 3, 4 );
// returns <Object>

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

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

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

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

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.

Notes

• If an environment supports Symbol.iterator and a provided iterator is iterable, the returned iterator is iterable.

Examples

var randu = require( '@stdlib/random-iter-randu' );
var iterUnshift = require( '@stdlib/iter-unshift' );

// Create a seeded iterator for generating pseudorandom numbers:
var rand = randu({
    'seed': 1234,
    'iter': 10
});

// Create an iterator with prepended values:
var it = iterUnshift( rand, 'beep', 'boop' );

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

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See Also

• @stdlib/iter-concat: create an iterator which iterates over the values of two or more iterators.
• @stdlib/iter-push: create an iterator which appends additional values to the end of a provided iterator.
• @stdlib/iter-shift: create an iterator which skips the first value of a provided iterator.

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Notice

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.

Community

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License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.