time-to-botec/squiggle/node_modules/@stdlib/utils/for-each-right/README.md

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# forEachRight

> Invoke a function for each element in a collection, iterating from the right to left.

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</section>

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<section class="usage">

## Usage

```javascript
var forEachRight = require( '@stdlib/utils/for-each-right' );
```

#### forEachRight( collection, fcn\[, thisArg ] )

Invokes a `function` for each element in a `collection`, iterating from right to left.

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

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

forEachRight( arr, log );
/* =>
    3: 4
    2: 3
    1: 2
    0: 1
*/
```

The invoked `function` is provided three arguments:

-   `value`: collection element
-   `index`: collection index
-   `collection`: input collection

Basic support for dynamic collections is provided. Note, however, that index incrementation is **not** guaranteed to be monotonically **decreasing**.

```javascript
var arr = [ 1, 2, 3, 4 ];
var i = 0;

function log1( value, index, collection ) {
    console.log( '%s: %d', index, value );
    i += 1;
    if ( index === 0 && collection.length < 10 ) {
        collection.unshift( i+1 );
    }
}

forEachRight( arr, log1 );
/* =>
    3: 4
    2: 3
    1: 2
    0: 1
    0: 5
    0: 6
    0: 7
    0: 8
    0: 9
    0: 10
*/

function log2( value, index, collection ) {
    console.log( '%s: %d', index, value );
    collection.pop();
}

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

forEachRight( arr, log2 );
/* =>
    3: 4
    1: 2
*/
```

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

```javascript
function sum( value ) {
    this.sum += value;
    this.count += 1;
}

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

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

forEachRight( arr, sum, context );

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`).

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

    -   The function returns the input `collection`.

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

        <!-- eslint-disable no-sparse-arrays -->

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

        var arr = [ 1, , , 4 ];

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

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

</section>

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## Examples

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

```javascript
var isEven = require( '@stdlib/assert/is-even' ).isPrimitive;
var forEachRight = require( '@stdlib/utils/for-each-right' );

var arr;
var i;

function log( value, index, collection ) {
    console.log( '%s: %d', index, value );
    i += 1;
    if ( isEven( i ) ) {
        collection.pop();
    } else {
        collection.unshift( i+1 );
    }
}

arr = new Array( 100 );
for ( i = arr.length-1; i >= 0; i-- ) {
    arr[ i ] = i;
}

i = 0;
forEachRight( arr, log );
```

</section>

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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-foreach]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach

</section>

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