# DataType
> Data type constructor.
## Usage
```javascript
var DataType = require( '@stdlib/ndarray/dtype-ctor' );
```
#### DataType( value\[, options] )
Returns a data type instance.
```javascript
var dt = new DataType( 'float64' );
// returns
```
The constructor supports the following parameters:
- **value**: data type value. Must be either a supported [data type][@stdlib/ndarray/dtypes] string, a [struct][@stdlib/dstructs/struct] constructor, or another data type instance.
- **options**: constructor options (_optional_).
The constructor supports the following options:
- **description**: data type description.
* * *
## Properties
#### DataType.prototype.alignment
Alignment (in bytes) for the data type.
```javascript
var dt = new DataType( 'float64' );
// returns
var v = dt.alignment;
// returns 8
```
If a data type does not have a known alignment, the returned value is `-1`.
#### DataType.prototype.byteLength
Size (in bytes) for the data type.
```javascript
var dt = new DataType( 'float64' );
// returns
var v = dt.byteLength;
// returns 8
```
If a data type does not have a known size, the returned value is `-1`.
#### DataType.prototype.byteOrder
Data type byte order.
```javascript
var dt = new DataType( 'float64' );
// returns
var v = dt.byteOrder;
// returns 'host'
```
The byte order may be one of the following values:
- **host**: host platform byte order.
- **little-endian**: little-endian byte order.
- **big-endian**: big-endian byte order.
#### DataType.prototype.char
Single letter character abbreviation for the data type.
```javascript
var dt = new DataType( 'float64' );
// returns
var v = dt.char;
// returns 'd'
```
If a data type does not have a corresponding single letter character abbreviation, the returned value is an empty string.
#### DataType.prototype.description
Data type description.
```javascript
var dt = new DataType( 'float64' );
// returns
var v = dt.description;
// returns '...'
```
If a data type does not have an associated description, the returned value is an empty string.
#### DataType.prototype.enum
Enumeration constant for the data type.
```javascript
var dt = new DataType( 'float64' );
// returns
var v = dt.enum;
// returns
```
If a data type does not have a corresponding known enumeration constant, the returned value is `-1`.
**Note**: enumeration constants should be treated as **opaque** values. One should **not** assume that a data type has a specific enumeration constant value.
#### DataType.prototype.value
Raw (original) data type value.
```javascript
var dt = new DataType( 'float64' );
// returns
var v = dt.value;
// returns 'float64'
```
* * *
## Methods
#### DataType.prototype.toJSON()
Returns a [JSON][json] representation of a `DataType` instance.
```javascript
var dt = new DataType( 'float64' );
// returns
var o = dt.toJSON();
// e.g., returns { 'type': 'DataType', 'value': 'float64', 'byteOrder': 'host', ... }
```
[`JSON.stringify()`][mdn-json-stringify] implicitly calls this method when stringifying a `DataType` instance.
#### DataType.prototype.toString()
Returns a string representation of a `DataType` instance.
```javascript
var dt = new DataType( 'float64' );
// returns
var str = dt.toString();
// returns 'float64'
```
#### DataType.prototype.valueOf()
Converts a `DataType` instance to a primitive value.
```javascript
var dt = new DataType( 'float64' );
// returns
var str = dt.valueOf();
// returns 'float64'
```
This method returns the same value as `#.toString()`.
* * *
## Examples
```javascript
var DataType = require( '@stdlib/ndarray/dtype-ctor' );
var dt = new DataType( 'complex128' );
console.log( 'type: %s', typeof dt );
// => 'type: object'
console.log( 'alignment: %d', dt.alignment );
// => 'alignment: 8'
console.log( 'byteLength: %d', dt.byteLength );
// => 'byteLength: 16'
console.log( 'byteOrder: %s', dt.byteOrder );
// => 'byteOrder: host'
console.log( 'char: %s', dt.char );
// => 'char: z'
console.log( 'JSON: %s', JSON.stringify( dt ) );
// e.g., => 'JSON: {"type": "DataType","value":"complex128","byteOrder":"host",...}'
```
[json]: http://www.json.org/
[mdn-json-stringify]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify
[@stdlib/ndarray/dtypes]: https://github.com/stdlib-js/ndarray/tree/main/dtypes
[@stdlib/dstructs/struct]: https://www.npmjs.com/package/@stdlib/dstructs-struct
[@stdlib/ndarray/ctor]: https://github.com/stdlib-js/ndarray/tree/main/ctor
[@stdlib/ndarray/dtype]: https://github.com/stdlib-js/ndarray/tree/main/dtype