214 lines
4.4 KiB
Markdown
214 lines
4.4 KiB
Markdown
<!--
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@license Apache-2.0
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Copyright (c) 2018 The Stdlib Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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-->
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# indexOf
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> Return the first index at which a given element can be found.
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<section class="usage">
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## Usage
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```javascript
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var indexOf = require( '@stdlib/utils/index-of' );
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```
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#### indexOf( arr, searchElement\[, fromIndex] )
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Returns the first index at which a given element can be found.
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```javascript
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var arr = [ 4, 3, 2, 1 ];
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var idx = indexOf( arr, 3 );
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// returns 1
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```
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If a `searchElement` is **not** present in an input `array`, the function returns `-1`.
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```javascript
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var arr = [ 4, 3, 2, 1 ];
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var idx = indexOf( arr, 5 );
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// returns -1
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```
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By default, the implementation searches an input `array` starting from the first element. To start searching from a different element, specify a `fromIndex`.
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```javascript
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var arr = [ 1, 2, 3, 4, 5, 2, 6 ];
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var idx = indexOf( arr, 2, 3 );
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// returns 5
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```
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If a `fromIndex` exceeds the input `array` length, the function returns `-1`.
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```javascript
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var arr = [ 1, 2, 3, 4, 2, 5 ];
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var idx = indexOf( arr, 2, 10 );
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// returns -1
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```
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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`).
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```javascript
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var arr = [ 1, 2, 3, 4, 5, 2, 6, 2 ];
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var idx = indexOf( arr, 2, -4 );
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// returns 5
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idx = indexOf( arr, 2, -1 );
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// returns 7
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```
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If `fromIndex` is less than `0` **and** its absolute value exceeds the input `array` length, the function searches the entire input `array`.
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```javascript
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var arr = [ 1, 2, 3, 4, 5, 2, 6 ];
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var idx = indexOf( arr, 2, -10 );
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// returns 1
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```
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The first argument is not limited to `arrays`, but may be any [array-like][@stdlib/assert/is-array-like] `object`.
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```javascript
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var str = 'bebop';
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var idx = indexOf( str, 'o' );
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// returns 3
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```
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</section>
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<!-- /.usage -->
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<section class="notes">
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## Notes
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- Search is performed using **strict equality** comparison. Thus,
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```javascript
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var arr = [ 1, [ 1, 2, 3 ], 3 ];
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var idx = indexOf( arr, [ 1, 2, 3 ] );
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// returns -1
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```
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- 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:
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```javascript
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// Locate the first element which is NaN...
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var arr = [ 1, NaN, 2, NaN ];
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var idx = indexOf( arr, NaN );
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// returns 1
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// Prototype properties may be searched as well...
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function Obj() {
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this[ 0 ] = 'beep';
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this[ 1 ] = 'boop';
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this[ 2 ] = 'woot';
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this[ 3 ] = 'bap';
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this.length = 4;
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return this;
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}
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Obj.prototype[ 2 ] = 'bop';
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var obj = new Obj();
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idx = indexOf( obj, 'bop' );
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// returns -1
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delete obj[ 2 ];
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idx = indexOf( obj, 'bop' );
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// returns 2
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```
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</section>
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<!-- /.notes -->
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<section class="examples">
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## Examples
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<!-- eslint no-undef: "error" -->
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```javascript
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var indexOf = require( '@stdlib/utils/index-of' );
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var arr;
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var obj;
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var str;
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var idx;
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var i;
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// Arrays...
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arr = new Array( 10 );
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for ( i = 0; i < arr.length; i++ ) {
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arr[ i ] = i * 10;
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}
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idx = indexOf( arr, 40 );
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console.log( idx );
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// => 4
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// Array-like objects...
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obj = {
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'0': 'beep',
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'1': 'boop',
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'2': 'bap',
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'3': 'bop',
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'length': 4
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};
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idx = indexOf( obj, 'bap' );
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console.log( idx );
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// => 2
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// Strings...
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str = 'beepboopbop';
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idx = indexOf( str, 'o' );
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console.log( idx );
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// => 5
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```
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</section>
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<!-- /.examples -->
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<section class="links">
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[ecma-262]: http://www.ecma-international.org/ecma-262/6.0/#sec-array.prototype.indexof
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[@stdlib/assert/is-array-like]: https://www.npmjs.com/package/@stdlib/assert-is-array-like
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</section>
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<!-- /.links -->
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