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Return the index of the last element which equals a provided search element.
To use in Observable,
lastIndexOf = require( 'https://cdn.jsdelivr.net/gh/stdlib-js/array-base-last-index-of@umd/browser.js' )To vendor stdlib functionality and avoid installing dependency trees for Node.js, you can use the UMD server build:
var lastIndexOf = require( 'path/to/vendor/umd/array-base-last-index-of/index.js' )To include the bundle in a webpage,
<script type="text/javascript" src="https://cdn.jsdelivr.net/gh/stdlib-js/array-base-last-index-of@umd/browser.js"></script>If no recognized module system is present, access bundle contents via the global scope:
<script type="text/javascript">
(function () {
window.lastIndexOf;
})();
</script>Returns the index of the last element which equals a provided search element.
var x = [ 1, 2, 3, 4, 5, 6 ];
var idx = lastIndexOf( x, 3, 5 );
// returns 2If 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 = lastIndexOf( x, 7, 5 );
// returns -1To begin searching from a specific index, provide a corresponding fromIndex argument.
var x = [ 1, 1, 2, 1, 2, 3, 3 ];
var idx = lastIndexOf( x, 2, 3 );
// returns 2If 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 = lastIndexOf( x, 2, -4 );
// returns 2-
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
lastIndexOfmethod, the function defers execution to that method and assumes that the method API has the following signature:x.lastIndexOf( searchElement, fromIndex ) -
If provided an array-like object without a
lastIndexOfmethod, 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,NaNvalues are considered distinct, and-0and+0are considered the same.
<!DOCTYPE html>
<html lang="en">
<body>
<script type="text/javascript" src="https://cdn.jsdelivr.net/gh/stdlib-js/array-base-last-index-of@umd/browser.js"></script>
<script type="text/javascript">
(function () {
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
})();
</script>
</body>
</html>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.
See LICENSE.
Copyright © 2016-2025. The Stdlib Authors.
