# Unary
> C API for registering a Node-API module exporting an ndarray interface for applying a unary callback to an input ndarray.
## Usage
```javascript
var headerDir = require( '@stdlib/ndarray/base/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/ndarray/base/napi/unary' );
console.log( headerDir );
// =>
```
* * *
## C APIs
### Usage
```c
#include "stdlib/ndarray/base/napi/unary.h"
```
#### stdlib_ndarray_napi_unary( env, info, \*obj )
Invokes an ndarray interface which applies a unary callback to an input ndarray based on provided JavaScript arguments.
```c
#include "stdlib/ndarray/base/function_object.h"
#include
// ...
static const struct ndarrayFunctionObject 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_ndarray_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 ndarrayFunctionObject*` ndarray [function object][@stdlib/ndarray/base/function-object].
```c
void stdlib_ndarray_napi_unary( napi_env env, napi_callback_info info, const struct ndarrayFunctionObject *obj );
```
#### STDLIB_NDARRAY_NAPI_MODULE_UNARY( obj )
Macro for registering a Node-API module exporting an ndarray interface for applying a unary callback to an input ndarray.
```c
#include "stdlib/ndarray/base/function_object.h"
// ...
// Create an ndarray function object:
static const struct ndarrayFunctionObject obj = {...};
// ...
// Register a Node-API module:
STDLIB_NDARRAY_NAPI_MODULE_UNARY( obj );
```
The macro expects the following arguments:
- **obj**: `struct ndarrayFunctionObject` ndarray [function object][@stdlib/ndarray/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:
- `X`: input ndarray data buffer (i.e., [typed array][mdn-typed-array]).
- `metaX`: `X` [serialized meta data][@stdlib/ndarray/base/serialize-meta-data].
- `Y`: destination ndarray data buffer (i.e., [typed array][mdn-typed-array]).
- `metaY`: `Y` [serialized meta data][@stdlib/ndarray/base/serialize-meta-data].
[mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray
[@stdlib/ndarray/base/function-object]: https://www.npmjs.com/package/@stdlib/ndarray/tree/main/base/function-object
[@stdlib/ndarray/base/serialize-meta-data]: https://www.npmjs.com/package/@stdlib/ndarray/tree/main/base/serialize-meta-data