# binaryOutputDataType
> Resolve the output ndarray [data type][@stdlib/ndarray/dtypes] for a binary function.
## Usage
```javascript
var binaryOutputDataType = require( '@stdlib/ndarray/base/binary-output-dtype' );
```
#### binaryOutputDataType( xdtype, ydtype, policy )
Resolves the output ndarray [data type][@stdlib/ndarray/dtypes] for a binary function according to a [data type policy][@stdlib/ndarray/output-dtype-policies].
```javascript
var dt = binaryOutputDataType( 'int32', 'float32', 'floating_point' );
var s = String( dt );
// returns 'float64'
```
The function supports the following parameters:
- **xdtype**: first input ndarray [data type][@stdlib/ndarray/dtypes].
- **ydtype**: second input ndarray [data type][@stdlib/ndarray/dtypes].
- **policy**: output [data type policy][@stdlib/ndarray/output-dtype-policies].
If `policy` is a [data type][@stdlib/ndarray/dtypes], the function always returns the `policy` value (i.e., the third argument).
```javascript
var dt = binaryOutputDataType( 'float32', 'float32', 'float64' );
var s = String( dt );
// returns 'float64'
dt = binaryOutputDataType( 'int32', 'int8', 'float64' );
s = String( dt );
// returns 'float64'
// ...
```
## Notes
- The function **always** applies [type promotion][@stdlib/ndarray/promotion-rules] to the provided data types, except for the following [data type policies][@stdlib/ndarray/output-dtype-policies]:
- `default`
- `default_index`
- `same`
- ``
## Examples
```javascript
var naryFunction = require( '@stdlib/utils/nary-function' );
var unzip = require( '@stdlib/utils/unzip' );
var nCartesianProduct = require( '@stdlib/array/base/n-cartesian-product' );
var dtypes = require( '@stdlib/ndarray/dtypes' );
var logEachMap = require( '@stdlib/console/log-each-map' );
var binaryOutputDataType = require( '@stdlib/ndarray/base/binary-output-dtype' );
// Get the list of real-valued data types:
var dt = dtypes( 'real' );
// Define a list of output data type policies:
var policies = [
'default',
'real',
'floating_point',
'complex_floating_point'
];
// Generate dtype-policy Cartesian products:
var args = nCartesianProduct( dt, dt, policies );
// Unzip the argument pair array:
args = unzip( args );
// Resolve output data types:
logEachMap( 'dtypes: (%7s, %7s). policy: %-24s. output dtype: %s.', args[ 0 ], args[ 1 ], args[ 2 ], naryFunction( binaryOutputDataType, 3 ) );
```
[@stdlib/ndarray/dtypes]: https://github.com/stdlib-js/ndarray/tree/main/dtypes
[@stdlib/ndarray/output-dtype-policies]: https://github.com/stdlib-js/ndarray/tree/main/output-dtype-policies
[@stdlib/ndarray/promotion-rules]: https://github.com/stdlib-js/ndarray/tree/main/promotion-rules