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lastIndexOfSameValue

Return the index of the last element which equals a provided search element according to the SameValue Algorithm.

Installation

npm install @stdlib/array-base-last-index-of-same-value

Alternatively,

• To load the package in a website via a script tag without installation and bundlers, use the ES Module available on the esm branch (see README).
• If you are using Deno, visit the deno branch (see README for usage intructions).
• For use in Observable, or in browser/node environments, use the Universal Module Definition (UMD) build available on the umd branch (see README).

The branches.md file summarizes the available branches and displays a diagram illustrating their relationships.

To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.

Usage

var lastIndexOfSameValue = require( '@stdlib/array-base-last-index-of-same-value' );

lastIndexOfSameValue( x, searchElement, fromIndex )

Returns the index of the last element which equals a provided search element according to the SameValue Algorithm.

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

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

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

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

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

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

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

var idx = lastIndexOfSameValue( 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.

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

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

Notes

• The function scans an input array from the starting index to the beginning of the array (i.e., backward).
• When searching for a search element, the function checks for equality using the SameValue Algorithm as specified in ECMAScript 5. As a consequence, NaN values are considered equal, and -0 and +0 are considered distinct.

Examples

var lastIndexOfSameValue = require( '@stdlib/array-base-last-index-of-same-value' );

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

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

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

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

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

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

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Notice

This package is part of 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, see the main project repository.

Community

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License

See LICENSE.

Copyright

Copyright © 2016-2025. The Stdlib Authors.