indexOf

Return the first index at which a given element can be found.

Installation

npm install @stdlib/utils-index-of

Usage

var indexOf = require( '@stdlib/utils-index-of' );

indexOf( arr, searchElement[, fromIndex] )

Returns the first index at which a given element can be found.

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

var idx = indexOf( arr, 3 );
// returns 1

If 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 -1

By 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 5

If 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 -1

If 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 7

If 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 1

The first argument is not limited to arrays, but may be any array-like object.

var str = 'bebop';

var idx = indexOf( str, 'o' );
// returns 3

Notes

• 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 array be searched by calling hasOwnProperty (thus, for most cases, incurring a performance penalty), and the standard does not accommodate a searchElement equal to NaN. 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

Examples

var indexOf = require( '@stdlib/utils-index-of' );

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

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

License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.