@stdlib/iter/every-by/README.md

Standard iterator utilities.

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# iterEveryBy

> Test whether every [iterated][mdn-iterator-protocol] value passes a test implemented by a predicate function.

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## 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
```

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

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## Notes

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

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## 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 );
```

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* * *

## 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>

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

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[@stdlib/iter/any-by]: https://github.com/stdlib-js/iter/tree/main/any-by

[@stdlib/iter/every]: https://github.com/stdlib-js/iter/tree/main/every

[@stdlib/iter/for-each]: https://github.com/stdlib-js/iter/tree/main/for-each

[@stdlib/iter/none-by]: https://github.com/stdlib-js/iter/tree/main/none-by

[@stdlib/iter/some-by]: https://github.com/stdlib-js/iter/tree/main/some-by

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