npm package: @stdlib/utils-every-by
Description: Test whether all elements in a collection 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 a collection pass 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/utils-every-by
```

</section>

<section class="usage">

## Usage

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

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

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

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

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

var bool = everyBy( arr, 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 arr = [ 1, -2, 3, 4 ];

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

The invoked `predicate` function is provided three arguments:

-   **value**: collection element.
-   **index**: collection index.
-   **collection**: input collection.

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

```javascript
function sum( value ) {
    if ( value < 0 ) {
        return false;
    }
    this.sum += value;
    this.count += 1;
    return true;
}

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

var context = {
    'sum': 0,
    'count': 0
};

var bool = everyBy( arr, sum, context );
// returns true

var mean = context.sum / context.count;
// returns 2.5
```

</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 `collection` may be either an [`Array`][mdn-array], [`Typed Array`][mdn-typed-array], or an array-like [`Object`][mdn-object] (excluding `strings` and `functions`).

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

    ```javascript
    function untrue() {
        return false;
    }
    var bool = everyBy( [], untrue );
    // returns true
    ```

-   The function differs from [`Array.prototype.every`][mdn-array-every] in the following ways:

    -   The function does **not** skip `undefined` elements.

        <!-- eslint-disable no-sparse-arrays, stdlib/doctest-marker -->

        ```javascript
        function log( value, index ) {
            console.log( '%s: %s', index, value );
            return true;
        }

        var arr = [ 1, , , 4 ];

        var bool = everyBy( arr, log );
        /* =>
            0: 1
            1: undefined
            2: undefined
            3: 4
        */
        ```

    -   The function provides limited support for dynamic collections (i.e., collections whose `length` changes during execution).

</section>

<!-- /.notes -->

<!-- Package usage examples. -->

<section class="examples">

## Examples

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

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

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

var bool;
var arr;
var i;

arr = new Array( 100 );
for ( i = 0; i < arr.length; i++ ) {
    arr[ i ] = randu();
}

bool = everyBy( arr, isPositive );
// returns <boolean>
```

</section>

<!-- /.examples -->

<!-- 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. -->

<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/utils-any-by`][@stdlib/utils/any-by]</span><span class="delimiter">: </span><span class="description">test whether at least one element in a collection passes a test implemented by a predicate function.</span>
-   <span class="package-name">[`@stdlib/utils-every-by-right`][@stdlib/utils/every-by-right]</span><span class="delimiter">: </span><span class="description">test whether all elements in a collection pass a test implemented by a predicate function, iterating from right to left.</span>
-   <span class="package-name">[`@stdlib/utils-for-each`][@stdlib/utils/for-each]</span><span class="delimiter">: </span><span class="description">invoke a function for each element in a collection.</span>
-   <span class="package-name">[`@stdlib/utils-none-by`][@stdlib/utils/none-by]</span><span class="delimiter">: </span><span class="description">test whether all elements in a collection fail a test implemented by a predicate function.</span>
-   <span class="package-name">[`@stdlib/utils-some-by`][@stdlib/utils/some-by]</span><span class="delimiter">: </span><span class="description">test whether a collection contains at least `n` elements which pass a test implemented by a predicate function.</span>

</section>

<!-- /.related -->

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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>

<!-- /.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/utils-every-by/tree/deno
[deno-readme]: https://github.com/stdlib-js/utils-every-by/blob/deno/README.md
[umd-url]: https://github.com/stdlib-js/utils-every-by/tree/umd
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[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/utils-every-by/main/LICENSE

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

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

[mdn-object]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object

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

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

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

[@stdlib/utils/every-by-right]: https://www.npmjs.com/package/@stdlib/utils-every-by-right

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

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

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

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