# Buffer Data Type Enumeration Constant
> Return the data type enumeration constant of an ndarray data buffer.
## Usage
```javascript
var dtypeEnum = require( '@stdlib/ndarray/base/buffer-dtype-enum' );
```
#### dtypeEnum( buffer )
Returns the [data type][@stdlib/ndarray/dtypes] enumeration constant of an ndarray data [buffer][@stdlib/ndarray/base/buffer-ctors].
```javascript
var Float64Array = require( '@stdlib/array/float64' );
var buf = new Float64Array( 10 );
var c = dtypeEnum( buf );
// returns
```
If provided an ndarray data [buffer][@stdlib/ndarray/base/buffer-ctors] having an unknown or unsupported [data type][@stdlib/ndarray/dtypes], the function returns `null`.
```javascript
var c = dtypeEnum( 'beep' );
// returns null
```
## Notes
- The principle use case for this function is JavaScript-C interoperability. In C, dtypes are assigned integer enumeration constants, not string values.
## Examples
```javascript
var dtypes = require( '@stdlib/ndarray/dtypes' );
var bufferCtors = require( '@stdlib/ndarray/base/buffer-ctors' );
var dtypeEnum = require( '@stdlib/ndarray/base/buffer-dtype-enum' );
// Get a list of supported ndarray buffer data types:
var DTYPES = dtypes( 'integer_and_generic' );
// Buffer length:
var len = 10;
// For each supported data type, create a buffer and retrieve its data type enumeration constant...
var ctor;
var i;
for ( i = 0; i < DTYPES.length; i++ ) {
ctor = bufferCtors( DTYPES[ i ] );
console.log( '%s => %d', DTYPES[ i ], dtypeEnum( new ctor( len ) ) );
}
// Try an array-like object...
var buf = {
'length': len
};
console.log( '%s => %s', 'generic', dtypeEnum( buf ) );
```
[@stdlib/ndarray/dtypes]: https://github.com/stdlib-js/ndarray/tree/main/dtypes
[@stdlib/ndarray/base/buffer-ctors]: https://github.com/stdlib-js/ndarray/tree/main/base/buffer-ctors