# Unary
> C API for registering a Node-API module exporting a strided array interface for applying a unary callback to an input strided array.
## Usage
```javascript
var headerDir = require( '@stdlib/strided/napi/unary' );
```
#### headerDir
Absolute file path for the directory containing header files for C APIs.
```javascript
var dir = headerDir;
// returns
```
## Examples
```javascript
var headerDir = require( '@stdlib/strided/napi/unary' );
console.log( headerDir );
// =>
```
* * *
## C APIs
### Usage
```c
#include "stdlib/strided/napi/unary.h"
```
#### stdlib_strided_napi_unary( env, info, \*obj )
Invokes a strided array interface which applies a unary callback to an input strided array based on provided JavaScript arguments.
```c
#include "stdlib/strided/base/function_object.h"
#include
// ...
static const struct StridedFunctionObject obj = {...};
// ...
/**
* Receives JavaScript callback invocation data.
*
* @param env environment under which the function is invoked
* @param info callback data
* @return Node-API value
*/
napi_value addon( napi_env env, napi_callback_info info ) {
stdlib_strided_napi_unary( env, info, &obj );
return NULL;
}
// ...
```
The function accepts the following arguments:
- **env**: `[in] napi_env` environment under which the function is invoked.
- **info**: `[in] napi_callback_info` callback data.
- **obj**: `[in] struct StridedFunctionObject*` strided array [function object][@stdlib/strided/base/function-object].
```c
void stdlib_strided_napi_unary( napi_env env, napi_callback_info info, const struct StridedFunctionObject *obj );
```
#### STDLIB_STRIDED_NAPI_MODULE_UNARY( obj )
Macro for registering a Node-API module exporting a strided array interface for applying a unary callback to an input strided array.
```c
#include "stdlib/strided/base/function_object.h"
// ...
// Create a strided function object:
static const struct StridedFunctionObject obj = {...};
// ...
// Register a Node-API module:
STDLIB_STRIDED_NAPI_MODULE_UNARY( obj );
```
The macro expects the following arguments:
- **obj**: `struct StridedFunctionObject` strided array [function object][@stdlib/strided/base/function-object].
When used, this macro should be used **instead of** `NAPI_MODULE`. The macro includes `NAPI_MODULE`, thus ensuring Node-API module registration.
### Notes
- The function expects that the callback `info` argument provides access to the following JavaScript arguments:
- `N`: number of indexed elements.
- `X`: input [typed array][mdn-typed-array].
- `strideX`: `X` stride length.
- `Y`: destination [typed array][mdn-typed-array].
- `strideY`: `Y` stride length.
[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray
[@stdlib/strided/base/function-object]: https://www.npmjs.com/package/@stdlib/strided/tree/main/base/function-object