npm package: @stdlib/array-base-every-by
Description: Test whether all elements in an array pass a test implemented by a predicate function.
Author: The Stdlib Authors
Latest version: 0.2.3

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# everyBy

[![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 all elements in an array pass a test implemented by a predicate function.

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<section class="intro">

</section>

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<!-- Package usage documentation. -->

<section class="installation">

## Installation

```bash
npm install @stdlib/array-base-every-by
```

</section>

<section class="usage">

## Usage

```javascript
var everyBy = require( '@stdlib/array-base-every-by' );
```

#### everyBy( x, predicate\[, thisArg] )

Tests whether all elements in an array pass a test implemented by a `predicate` function.

```javascript
function isPositive( value ) {
    return ( value > 0 );
}

var x = [ 1, 2, 3, 4 ];

var bool = everyBy( x, isPositive );
// returns true
```

If a `predicate` function returns a non-truthy value, the function **immediately** returns `false`.

```javascript
function isPositive( value ) {
    return ( value > 0 );
}

var x = [ 1, -2, 3, 4 ];

var bool = everyBy( x, isPositive );
// returns false
```

The `predicate` function is provided three arguments:

-   **value**: current array element.
-   **index**: current array element index.
-   **arr**: input array.

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

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

var x = [ 1, 2, -3, 4 ];

var context = {
    'count': 0
};

var bool = everyBy( x, predicate, context );
// returns false

var cnt = context.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

-   If provided an array-like object having an `every` method, the function defers execution to that method and assumes that the method API has the following signature:

    ```text
    x.every( predicate, thisArg )
    ```

-   If provided an array-like object without an `every` method, the function performs a linear scan and returns immediately upon encountering a non-truthy return value. Unlike [`Array.prototype.every`][mdn-array-every], when performing a linear scan, the function does **not** skip `undefined` elements.

-   If provided an empty array, the function returns `true`.

</section>

<!-- /.notes -->

<!-- Package usage examples. -->

<section class="examples">

## Examples

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

```javascript
var discreteUniform = require( '@stdlib/random-array-discrete-uniform' );
var isPositiveInteger = require( '@stdlib/assert-is-positive-integer' ).isPrimitive;
var naryFunction = require( '@stdlib/utils-nary-function' );
var everyBy = require( '@stdlib/array-base-every-by' );

var x = discreteUniform( 10, 0, 10, {
    'dtype': 'int32'
});
// returns <Int32Array>

var out = everyBy( x, naryFunction( isPositiveInteger, 1 ) );
// returns <boolean>
```

</section>

<!-- /.examples -->

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</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-url]: https://npmjs.org/package/@stdlib/array-base-every-by

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

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

[mdn-array-every]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/every

</section>

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