# propertyNames
> Return an array of an object's own enumerable and non-enumerable property names.
## Usage
```javascript
var propertyNames = require( '@stdlib/utils/property-names' );
```
#### propertyNames( obj )
Returns an `array` of an object's own enumerable and non-enumerable property names.
```javascript
var obj = {
'a': 1,
'b': 2
};
var keys = propertyNames( obj );
// e.g., returns [ 'a', 'b' ]
```
## Notes
- Name order is not guaranteed, as `object` key enumeration is not specified according to the [ECMAScript specification][ecma-262-for-in]. In practice, however, most engines use insertion order to sort an `object`'s keys, thus allowing for deterministic extraction.
- In contrast to the built-in `Object.getOwnPropertyNames()`, if provided `null` or `undefined`, the function returns an empty `array`, rather than throwing an error.
## Examples
```javascript
var defineProperty = require( '@stdlib/utils/define-property' );
var propertyNames = require( '@stdlib/utils/property-names' );
function Foo() {
this.beep = 'boop';
this.a = {
'b': 'c'
};
defineProperty( this, 'baz', {
'value': 'qux',
'configurable': true,
'writable': true,
'enumerable': false
});
return this;
}
Foo.prototype.foo = [ 'bar' ];
var obj = new Foo();
var keys = propertyNames( obj );
console.log( keys );
// e.g., => [ 'beep', 'a', 'baz' ]
```
[ecma-262-for-in]: http://www.ecma-international.org/ecma-262/5.1/#sec-12.6.4