npm package: @stdlib/iter-cuevery-by
Description: Create an iterator which cumulatively tests whether every iterated value passes a test implemented by a predicate function.
Author: The Stdlib Authors
Latest version: 0.1.1

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# iterCuEveryBy

[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url] <!-- [![dependencies][dependencies-image]][dependencies-url] -->

> Create an iterator which cumulatively tests whether every iterated value passes a test implemented by a predicate function.

<!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. -->

<section class="intro">

</section>

<!-- /.intro -->

<!-- Package usage documentation. -->

<section class="installation">

## Installation

```bash
npm install @stdlib/iter-cuevery-by
```

</section>

<section class="usage">

## Usage

```javascript
var iterCuEveryBy = require( '@stdlib/iter-cuevery-by' );
```

#### iterCuEveryBy( iterator, predicate\[, thisArg] )

Returns an [iterator][mdn-iterator-protocol] which cumulatively tests whether every iterated value passes a test implemented by a `predicate` function.

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

function predicate( v ) {
    return ( v > 0 );
}

var arr = array2iterator( [ 1, 1, 1, 0, 1 ] );

var it = iterCuEveryBy( arr, predicate );

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

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

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

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

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

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

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

-   **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.
-   **return**: function which closes an [iterator][mdn-iterator-protocol] and returns a single (optional) argument in an [iterator][mdn-iterator-protocol] protocol-compliant object.

A `predicate` function is provided two arguments:

-   **value**: iterated value.
-   **index**: iteration index (zero-based).

To set the `predicate` function execution context, provide a `thisArg`.

<!-- eslint-disable no-invalid-this -->

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

function predicate( v ) {
    this.count += 1;
    return ( v > 0 );
}

var ctx = {
    'count': 0
};

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

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

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

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

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

var count = ctx.count;
// returns 4
```

</section>

<!-- /.usage -->

<!-- Package usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->

<section class="notes">

## Notes

-   A `predicate` function is invoked for each iterated value until the first falsy `predicate` function return value. Upon encountering the first falsy return value, the returned iterator ceases to invoke the `predicate` function and returns `false` for each subsequent iterated value of the provided input `iterator`.

</section>

<!-- /.notes -->

<!-- Package usage examples. -->

<section class="examples">

## Examples

<!-- eslint no-undef: "error" -->

```javascript
var randu = require( '@stdlib/random-iter-randu' );
var iterCuEveryBy = require( '@stdlib/iter-cuevery-by' );

function threshold( r ) {
    return ( r > 0.05 );
}

// Create an iterator which generates uniformly distributed pseudorandom numbers:
var opts = {
    'iter': 100
};
var riter = randu( opts );

// Create an iterator which cumulatively tests whether every iterated value passes a test:
var it = iterCuEveryBy( riter, threshold );

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

</section>

<!-- /.examples -->

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<section class="references">

</section>

<!-- /.references -->

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<section class="related">

</section>

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<section class="main-repo" >

* * *

## Notice

This package is part of [stdlib][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][stdlib], see the main project [repository][stdlib].

#### Community

[![Chat][chat-image]][chat-url]

---

## License

See [LICENSE][stdlib-license].


## Copyright

Copyright &copy; 2016-2026. The Stdlib [Authors][stdlib-authors].

</section>

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[npm-image]: http://img.shields.io/npm/v/@stdlib/iter-cuevery-by.svg
[npm-url]: https://npmjs.org/package/@stdlib/iter-cuevery-by

[test-image]: https://github.com/stdlib-js/iter-cuevery-by/actions/workflows/test.yml/badge.svg?branch=v0.1.1
[test-url]: https://github.com/stdlib-js/iter-cuevery-by/actions/workflows/test.yml?query=branch:v0.1.1

[coverage-image]: https://img.shields.io/codecov/c/github/stdlib-js/iter-cuevery-by/main.svg
[coverage-url]: https://codecov.io/github/stdlib-js/iter-cuevery-by?branch=main

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[stdlib]: https://github.com/stdlib-js/stdlib

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[umd]: https://github.com/umdjs/umd
[es-module]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules

[deno-url]: https://github.com/stdlib-js/iter-cuevery-by/tree/deno
[deno-readme]: https://github.com/stdlib-js/iter-cuevery-by/blob/deno/README.md
[umd-url]: https://github.com/stdlib-js/iter-cuevery-by/tree/umd
[umd-readme]: https://github.com/stdlib-js/iter-cuevery-by/blob/umd/README.md
[esm-url]: https://github.com/stdlib-js/iter-cuevery-by/tree/esm
[esm-readme]: https://github.com/stdlib-js/iter-cuevery-by/blob/esm/README.md
[branches-url]: https://github.com/stdlib-js/iter-cuevery-by/blob/main/branches.md

[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/iter-cuevery-by/main/LICENSE

[mdn-iterator-protocol]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterator_protocol

</section>

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