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Return the first index at which a given element can be found.
To use in Observable,
indexOf = require( 'https://cdn.jsdelivr.net/gh/stdlib-js/utils-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 indexOf = require( 'path/to/vendor/umd/utils-index-of/index.js' )To include the bundle in a webpage,
<script type="text/javascript" src="https://cdn.jsdelivr.net/gh/stdlib-js/utils-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.indexOf;
})();
</script>Returns the first index at which a given element can be found.
var arr = [ 4, 3, 2, 1 ];
var idx = indexOf( arr, 3 );
// returns 1If a searchElement is not present in an input array, the function returns -1.
var arr = [ 4, 3, 2, 1 ];
var idx = indexOf( arr, 5 );
// returns -1By default, the implementation searches an input array starting from the first element. To start searching from a different element, specify a fromIndex.
var arr = [ 1, 2, 3, 4, 5, 2, 6 ];
var idx = indexOf( arr, 2, 3 );
// returns 5If a fromIndex exceeds the input array length, the function returns -1.
var arr = [ 1, 2, 3, 4, 2, 5 ];
var idx = indexOf( arr, 2, 10 );
// returns -1If a fromIndex is less than 0, the starting index is determined relative to the last index (with the last index being equivalent to fromIndex = -1).
var arr = [ 1, 2, 3, 4, 5, 2, 6, 2 ];
var idx = indexOf( arr, 2, -4 );
// returns 5
idx = indexOf( arr, 2, -1 );
// returns 7If fromIndex is less than 0 and its absolute value exceeds the input array length, the function searches the entire input array.
var arr = [ 1, 2, 3, 4, 5, 2, 6 ];
var idx = indexOf( arr, 2, -10 );
// returns 1The first argument is not limited to arrays, but may be any array-like object.
var str = 'bebop';
var idx = indexOf( str, 'o' );
// returns 3-
Search is performed using strict equality comparison. Thus,
var arr = [ 1, [ 1, 2, 3 ], 3 ]; var idx = indexOf( arr, [ 1, 2, 3 ] ); // returns -1
-
This implementation is not ECMAScript Standard compliant. Notably, the standard specifies that an
arraybe searched by callinghasOwnProperty(thus, for most cases, incurring a performance penalty), and the standard does not accommodate asearchElementequal toNaN. In this implementation, the following is possible:// Locate the first element which is NaN... var arr = [ 1, NaN, 2, NaN ]; var idx = indexOf( arr, NaN ); // returns 1 // Prototype properties may be searched as well... function Obj() { this[ 0 ] = 'beep'; this[ 1 ] = 'boop'; this[ 2 ] = 'woot'; this[ 3 ] = 'bap'; this.length = 4; return this; } Obj.prototype[ 2 ] = 'bop'; var obj = new Obj(); idx = indexOf( obj, 'bop' ); // returns -1 delete obj[ 2 ]; idx = indexOf( obj, 'bop' ); // returns 2
<!DOCTYPE html>
<html lang="en">
<body>
<script type="text/javascript" src="https://cdn.jsdelivr.net/gh/stdlib-js/utils-index-of@umd/browser.js"></script>
<script type="text/javascript">
(function () {
var arr;
var obj;
var str;
var idx;
var i;
// Arrays...
arr = new Array( 10 );
for ( i = 0; i < arr.length; i++ ) {
arr[ i ] = i * 10;
}
idx = indexOf( arr, 40 );
console.log( idx );
// => 4
// Array-like objects...
obj = {
'0': 'beep',
'1': 'boop',
'2': 'bap',
'3': 'bop',
'length': 4
};
idx = indexOf( obj, 'bap' );
console.log( idx );
// => 2
// Strings...
str = 'beepboopbop';
idx = indexOf( str, 'o' );
console.log( idx );
// => 5
})();
</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.
