@stdlib/array/base/index-of/README.md

Arrays.

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# indexOf

> Return the index of the first element which equals a provided search element.

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## Usage

```javascript
var indexOf = require( '@stdlib/array/base/index-of' );
```

#### indexOf( x, searchElement, fromIndex, equalNaNs )

Returns the index of the first element which equals a provided search element.

```javascript
var x = [ 1, 2, 3, 4, 5, 6 ];

var idx = indexOf( x, 3, 0, false );
// returns 2
```

If the function is unable to find an element which equals a provided search element, the function returns `-1`.

```javascript
var x = [ 1, 2, 3, 4, 5, 6 ];

var idx = indexOf( x, 7, 0, false );
// returns -1
```

To begin searching from specific index, provide a non-zero `fromIndex` argument.

```javascript
var x = [ 1, 1, 2, 1, 2, 3, 3 ];

var idx = indexOf( x, 2, 3, false );
// returns 4
```

If `fromIndex` is less than zero, the starting index is resolved relative to the last array element, with the last array element corresponding to `fromIndex = -1`.

```javascript
var x = [ 1, 1, 2, 1, 2, 3, 3 ];

var idx = indexOf( x, 2, -4, false );
// returns 4
```

When searching for a search element, the function checks for strict equality. As a consequence, `NaN` values are considered distinct. In order to resolve the first element which is `NaN`, set the `equalNaNs` argument to `true`.

```javascript
var x = [ 1, 2, 3, NaN, 5, 6 ];

var idx = indexOf( x, NaN, 0, false );
// returns -1

idx = indexOf( x, NaN, 0, true );
// returns 3
```

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## Notes

-   If provided an array-like object having an `indexOf` method and `equalNaNs` is `false`, the function defers execution to that method and assumes that the method API has the following signature:

    ```text
    x.indexOf( searchElement, fromIndex )
    ```

-   If provided an array-like object without an `indexOf` method or if `equalNaNs` is `true`, the function performs a linear scan and returns immediately upon finding a match.

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## Examples

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```javascript
var indexOf = require( '@stdlib/array/base/index-of' );

var x = [ 'foo', 'bar', 'beep', 'boop', 'foo', 'bar' ];

var idx = indexOf( x, 'beep', 0, false );
// returns 2

idx = indexOf( x, 'bop', 0, false );
// returns -1

idx = indexOf( x, 'foo', 1, false );
// returns 4

idx = indexOf( x, 'foo', -4, false );
// returns 4

idx = indexOf( x, 'foo', 5, false );
// returns -1
```

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