indexOf

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

Installation

1$ npm install utils-indexof

Usage

1var indexOf = require( 'utils-indexof' );

indexOf( arr, searchElement[, fromIndex] )

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

1var arr = [ 4, 3, 2, 1 ];
2
3var idx = indexOf( arr, 3 );
4// returns 1

If a searchElement is not present in an input array, the function returns -1.

1var arr = [ 4, 3, 2, 1 ];
2
3var idx = indexOf( arr, 5 );
4// returns -1

By default, the implementation searches an input array beginning from the first element. To start searching from a different element, specify a fromIndex.

1var arr = [ 1, 2, 3, 4, 5, 2, 6 ];
2
3var idx = indexOf( arr, 2, 3 );
4// returns 5

If a fromIndex exceeds the input array length, the function returns -1.

1var arr = [ 1, 2, 3, 4, 2, 5 ];
2
3var idx = indexOf( arr, 2, 10 );
4// 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).

1var arr = [ 1, 2, 3, 4, 5, 2, 6, 2 ];
2
3var idx = indexOf( arr, 2, -4 );
4// returns 5
5
6idx = indexOf( arr, 2, -1 );
7// returns 7

If fromIndex is less than 0 and its absolute value exceeds the input array length, the function searches the entire input array.

1var arr = [ 1, 2, 3, 4, 5, 2, 6 ];
2
3var idx = indexOf( arr, 2, -10 );
4// returns 1

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

1var str = 'bebop';
2
3var idx = indexOf( str, 'o' );
4// returns 3

Notes

• Search is performed using strict equality comparison. Thus,

  1var arr = [ 1, [1,2,3], 3 ];
  2
  3var idx = indexOf( arr, [1,2,3] );
  4// 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:

  1// Locate the first element which is NaN...
  2var arr = [ 1, NaN, 2, NaN ];
  3
  4var idx = indexOf( arr, NaN );
  5// returns 1
  6
  7// Prototype properties may be searched as well...
  8function Obj() {
  9	this[ 0 ] = 'beep';
  10	this[ 1 ] = 'boop';
  11	this[ 2 ] = 'woot';
  12	this[ 3 ] = 'bap';
  13	this.length = 4;
  14	return this;
  15}
  16Obj.prototype[ 2 ] = 'bop';
  17
  18var obj = new Obj();
  19
  20idx = indexOf( obj, 'bop' );
  21// returns -1
  22
  23delete obj[ 2 ];
  24
  25idx = indexOf( obj, 'bop' );
  26// returns 2

Examples

1var indexOf = require( 'utils-indexof' );
2
3var arr;
4var obj;
5var str;
6var idx;
7var i;
8
9// Arrays...
10arr = new Array( 10 );
11for ( i = 0; i < arr.length; i++ ) {
12	arr[ i ] = i * 10;
13}
14idx = indexOf( arr, 40 );
15
16console.log( idx );
17// returns 4
18
19
20// Array-like objects...
21obj = {
22	'0': 'beep',
23	'1': 'boop',
24	'2': 'bap',
25	'3': 'bop',
26	'length': 4
27};
28
29idx = indexOf( obj, 'bap' );
30
31console.log( idx );
32// returns 2
33
34
35// Strings...
36str = 'beepboopbop';
37
38idx = indexOf( str, 'o' );
39
40console.log( idx );
41// returns 5

To run the example code from the top-level application directory,

1$ node ./examples/index.js

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Tests

Unit

This repository uses tape for unit tests. To run the tests, execute the following command in the top-level application directory:

1$ make test

All new feature development should have corresponding unit tests to validate correct functionality.

Test Coverage

This repository uses Istanbul as its code coverage tool. To generate a test coverage report, execute the following command in the top-level application directory:

1$ make test-cov

Istanbul creates a ./reports/coverage directory. To access an HTML version of the report,

1$ make view-cov

Browser Support

This repository uses Testling for browser testing. To run the tests in a (headless) local web browser, execute the following command in the top-level application directory:

1$ make test-browsers

To view the tests in a local web browser,

1$ make view-browser-tests

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License

MIT license.

Copyright

Copyright © 2016. Athan Reines.