@stdlib/assert/contains/README.md

Standard assertion utilities.

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# Contains

> Test if an array-like value contains a search value.

<section class="intro">

</section>

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<section class="usage">

## Usage

```javascript
var contains = require( '@stdlib/assert/contains' );
```

#### contains( val, searchValue\[, position] )

Tests if `val` contains a search value. When `val` is a `string`, the function checks whether the characters of a search string are found in the input string.

```javascript
var v = contains( 'Hello World', 'World' );
// returns true
```

When `val` is an `array-like` object, but not a `string`, the function checks whether the input value contains an element strictly equal to the specified search value.

```javascript
var arr = [ null, NaN, 2, 'abc', {} ];

var v = contains( arr, NaN ); // NaNs are considered equal
// returns true

v = contains( arr, {} );
// returns false

v = contains( arr, 'ab' );
// returns false
```

Search is case-sensitive.

```javascript
var v = contains( 'Hello World', 'world' );
// returns false
```

To start searching at a specified index, provide a `position` argument.

```javascript
var v = contains( 'Hello World', 'Hello', 6 );
// returns false

v = contains( [ true, NaN, false ], true, 1 );
// returns false
```

If not provided an `array-like` object, the function throws an error.

<!-- run throws: true -->

```javascript
var v = contains( false, 'abc' );
// throws <TypeError>
```

If not provided an integer-valued `position` argument, the function throws an error.

<!-- run throws: true -->

```javascript
var v = contains( 'hello', 'e', 2.5 );
// throws <TypeError>
```

</section>

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<section class="notes">

* * *

## Notes

-   For `strings`, the function is modeled after [String.prototype.includes][mdn-includes], part of the ECMAScript 6 specification. This function is different from a call to `String.prototype.includes.call` insofar as type-checking is performed for all arguments.
-   The function does **not** distinguish between positive and negative zero.
-   If `position < 0`, the search is performed for the entire input array or string.

</section>

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<section class="examples">

## Examples

<!-- eslint no-undef: "error" -->

```javascript
var contains = require( '@stdlib/assert/contains' );

var bool = contains( 'last man standing', 'stand' );
// returns true

bool = contains( [ 1, 2, 3, 4 ], 2 );
// returns true

bool = contains( 'presidential election', 'president' );
// returns true

bool = contains( [ NaN, 2, 3, 4 ], NaN );
// returns true

bool = contains( 'javaScript', 'js' );
// returns false

bool = contains( 'Hidden Treasures', '' );
// returns true
```

</section>

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<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->

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</section>

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<section class="links">

[mdn-includes]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/includes

</section>

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