JarCastingindexOf
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
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
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
Copyright
Copyright © 2016. Athan Reines.