npm package: @stdlib/array-base-last-index-of
Description: Return the index of the last element which equals a provided search element.
Author: The Stdlib Authors
Latest version: 0.3.1

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# lastIndexOf

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> Return the index of the last element which equals a provided search element.

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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-last-index-of
```

</section>

<section class="usage">

## Usage

```javascript
var lastIndexOf = require( '@stdlib/array-base-last-index-of' );
```

#### lastIndexOf( x, searchElement, fromIndex )

Returns the index of the last element which equals a provided search element.

```javascript
var x = [ 1, 2, 3, 4, 5, 6 ];

var idx = lastIndexOf( x, 3, 5 );
// returns 2
```

If the function is unable to find an element which equals a provided search element, the function returns `-1`.

```javascript
var x = [ 1, 2, 3, 4, 5, 6 ];

var idx = lastIndexOf( x, 7, 5 );
// returns -1
```

To begin searching from a specific index, provide a corresponding `fromIndex` argument.

```javascript
var x = [ 1, 1, 2, 1, 2, 3, 3 ];

var idx = lastIndexOf( x, 2, 3 );
// returns 2
```

If `fromIndex` is less than zero, the starting index is resolved relative to the last array element, with the last array element corresponding to `fromIndex = -1`.

```javascript
var x = [ 1, 1, 2, 1, 2, 3, 3 ];

var idx = lastIndexOf( x, 2, -4 );
// returns 2
```

</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

-   The function scans an input array from the starting index to the beginning of the array (i.e., backward).

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

    ```text
    x.lastIndexOf( searchElement, fromIndex )
    ```

-   If provided an array-like object without a `lastIndexOf` method, the function performs a linear scan and returns immediately upon finding a match.

-   When searching for a search element, the function checks for equality using the strict equality operator `===`. As a consequence, `NaN` values are considered distinct, and `-0` and `+0` are considered the same.

</section>

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<!-- Package usage examples. -->

<section class="examples">

## Examples

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

```javascript
var lastIndexOf = require( '@stdlib/array-base-last-index-of' );

var x = [ 'foo', 'bar', 'beep', 'boop', 'foo', 'bar' ];

var idx = lastIndexOf( x, 'beep', 5 );
// returns 2

idx = lastIndexOf( x, 'bop', 5 );
// returns -1

idx = lastIndexOf( x, 'foo', 5 );
// returns 4

idx = lastIndexOf( x, 'foo', -3 );
// returns 0

idx = lastIndexOf( x, 'foo', -50 );
// returns -1
```

</section>

<!-- /.examples -->

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* * *

## 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

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---

## License

See [LICENSE][stdlib-license].


## Copyright

Copyright &copy; 2016-2026. The Stdlib [Authors][stdlib-authors].

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