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utils-indexof

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  • License MIT

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

Package Exports

  • utils-indexof

This package does not declare an exports field, so the exports above have been automatically detected and optimized by JSPM instead. If any package subpath is missing, it is recommended to post an issue to the original package (utils-indexof) to support the "exports" field. If that is not possible, create a JSPM override to customize the exports field for this package.

Readme

indexOf

NPM version Build Status Coverage Status Dependencies

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

Installation

$ npm install utils-indexof

Usage

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

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 beginning 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( '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,

$ node ./examples/index.js

Tests

Unit

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

$ 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:

$ make test-cov

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

$ 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:

$ make test-browsers

To view the tests in a local web browser,

$ make view-browser-tests

License

MIT license.

Copyright © 2016. Athan Reines.