time-to-botec/squiggle/node_modules/@stdlib/utils/every-by/README.md

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# everyBy

> Test whether all elements in a collection pass a test implemented by a predicate function.

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</section>

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## 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 `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
```

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## 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).

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## 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>
```

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[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

</section>

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