Returns the first index at which a given element can be found.
npm install utils-indexofindexOf
===
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> Returns the first index at which a given element can be found.
`` bash`
$ npm install utils-indexof
` javascript`
var indexOf = require( 'utils-indexof' );
#### indexOf( arr, searchElement[, fromIndex] )
Returns the first index at which a given element can be found.
` javascript
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.
` javascript
var arr = [ 4, 3, 2, 1 ];
var idx = indexOf( arr, 5 );
// 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.
` javascript
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.
` javascript
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).
` javascript
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.
` javascript
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][validate.io-array-like] object.
` javascript
var str = 'bebop';
var idx = indexOf( str, 'o' );
// returns 3
`
* Search is performed using __strict equality__ comparison. Thus,
` javascript
var arr = [ 1, [1,2,3], 3 ];
var idx = indexOf( arr, [1,2,3] );
// returns -1
`
* This implementation is __not__ [ECMAScript Standard][ecma-262] compliant. Notably, the [standard][ecma-262] specifies that an array be searched by calling hasOwnProperty (thus, for most cases, incurring a performance penalty), and the [standard][ecma-262] does __not__ accommodate a searchElement equal to NaN. In this implementation, the following is possible:
` javascript
// 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
`
` javascript
var indexOf = require( 'utils-indexof' );
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 );
// returns 4
// Array-like objects...
obj = {
'0': 'beep',
'1': 'boop',
'2': 'bap',
'3': 'bop',
'length': 4
};
idx = indexOf( obj, 'bap' );
console.log( idx );
// returns 2
// Strings...
str = 'beepboopbop';
idx = indexOf( str, 'o' );
console.log( idx );
// returns 5
`
To run the example code from the top-level application directory,
` bash`
$ node ./examples/index.js
---
This repository uses [tape][tape] for unit tests. To run the tests, execute the following command in the top-level application directory:
` bash`
$ make test
All new feature development should have corresponding unit tests to validate correct functionality.
This repository uses [Istanbul][istanbul] as its code coverage tool. To generate a test coverage report, execute the following command in the top-level application directory:
` bash`
$ make test-cov
Istanbul creates a ./reports/coverage directory. To access an HTML version of the report,
` bash`
$ make view-cov
This repository uses [Testling][testling] for browser testing. To run the tests in a (headless) local web browser, execute the following command in the top-level application directory:
` bash`
$ make test-browsers
To view the tests in a local web browser,
` bash``
$ make view-browser-tests
---
Copyright © 2016. Athan Reines.
[npm-image]: http://img.shields.io/npm/v/utils-indexof.svg
[npm-url]: https://npmjs.org/package/utils-indexof
[build-image]: http://img.shields.io/travis/kgryte/utils-indexof/master.svg
[build-url]: https://travis-ci.org/kgryte/utils-indexof
[coverage-image]: https://img.shields.io/codecov/c/github/kgryte/utils-indexof/master.svg
[coverage-url]: https://codecov.io/github/kgryte/utils-indexof?branch=master
[dependencies-image]: http://img.shields.io/david/kgryte/utils-indexof.svg
[dependencies-url]: https://david-dm.org/kgryte/utils-indexof
[dev-dependencies-image]: http://img.shields.io/david/dev/kgryte/utils-indexof.svg
[dev-dependencies-url]: https://david-dm.org/dev/kgryte/utils-indexof
[github-issues-image]: http://img.shields.io/github/issues/kgryte/utils-indexof.svg
[github-issues-url]: https://github.com/kgryte/utils-indexof/issues
[tape]: https://github.com/substack/tape
[istanbul]: https://github.com/gotwarlost/istanbul
[testling]: https://ci.testling.com
[ecma-262]: http://www.ecma-international.org/ecma-262/6.0/#sec-array.prototype.indexof
[validate.io-array-like]: https://github.com/validate.io/array-like