npm package: @stdlib/iter-every-by
Description: Test whether every iterated value passes a test implemented by a predicate function.
Author: The Stdlib Authors
Latest version: 0.2.3

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<details>
  <summary>
    About stdlib...
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# iterEveryBy

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

> Test whether every [iterated][mdn-iterator-protocol] 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-every-by
```

</section>

<section class="usage">

## Usage

```javascript
var iterEveryBy = require( '@stdlib/iter-every-by' );
```

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

Tests whether every [iterated][mdn-iterator-protocol] 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, 1, 1 ] );

var bool = iterEveryBy( arr, predicate );
// returns true
```

If a provided [`iterator`][mdn-iterator-protocol] does not return any iterated values, the function returns `true`.

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

function predicate() {
    return true;
}

var bool = iterEveryBy( array2iterator( [] ), predicate );
// returns true
```

A `predicate` function is provided two arguments:

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

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

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

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

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

var ctx = {
    'count': 0
};

var bool = iterEveryBy( arr, predicate, ctx );
// returns false

var n = ctx.count;
// returns 3
```

</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

-   The function immediately returns upon encountering a falsy return value.

</section>

<!-- /.notes -->

<!-- Package usage examples. -->

<section class="examples">

## Examples

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

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

function threshold( r ) {
    return ( r < 0.99 );
}

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

// Determine if all values are below a threshold:
var bool = iterEveryBy( riter, threshold );
// returns <boolean>

console.log( bool );
```

</section>

<!-- /.examples -->

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<section class="references">

</section>

<!-- /.references -->

<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->

<section class="related">

* * *

## See Also

-   <span class="package-name">[`@stdlib/iter-any-by`][@stdlib/iter/any-by]</span><span class="delimiter">: </span><span class="description">test whether at least one iterated value passes a test implemented by a predicate function.</span>
-   <span class="package-name">[`@stdlib/iter-every`][@stdlib/iter/every]</span><span class="delimiter">: </span><span class="description">test whether all iterated values are truthy.</span>
-   <span class="package-name">[`@stdlib/iter-for-each`][@stdlib/iter/for-each]</span><span class="delimiter">: </span><span class="description">create an iterator which invokes a function for each iterated value before returning the iterated value.</span>
-   <span class="package-name">[`@stdlib/iter-none-by`][@stdlib/iter/none-by]</span><span class="delimiter">: </span><span class="description">test whether every iterated value fails a test implemented by a predicate function.</span>
-   <span class="package-name">[`@stdlib/iter-some-by`][@stdlib/iter/some-by]</span><span class="delimiter">: </span><span class="description">test whether at least `n` iterated values pass a test implemented by a predicate function.</span>

</section>

<!-- /.related -->

<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->


<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>

<!-- /.stdlib -->

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

[test-image]: https://github.com/stdlib-js/iter-every-by/actions/workflows/test.yml/badge.svg?branch=v0.2.3
[test-url]: https://github.com/stdlib-js/iter-every-by/actions/workflows/test.yml?query=branch:v0.2.3

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

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

[stdlib-authors]: https://github.com/stdlib-js/stdlib/graphs/contributors

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

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

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

<!-- <related-links> -->

[@stdlib/iter/any-by]: https://www.npmjs.com/package/@stdlib/iter-any-by

[@stdlib/iter/every]: https://www.npmjs.com/package/@stdlib/iter-every

[@stdlib/iter/for-each]: https://www.npmjs.com/package/@stdlib/iter-for-each

[@stdlib/iter/none-by]: https://www.npmjs.com/package/@stdlib/iter-none-by

[@stdlib/iter/some-by]: https://www.npmjs.com/package/@stdlib/iter-some-by

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</section>

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