function unique( arr ) {
	var obj;
	var i;

	obj = {};
	for ( i = 0; i < arr.length; i++ ) {
		if ( !hasOwnProp( obj, arr[ i ] ) ) {
			obj[ arr[ i ] ] = true;
		}
	}
	return objectKeys( obj );
}
Returns an array of unique items.

@private
@param {Array} arr - input array
@returns {Array} array containing only unique items