CodeIgniter - Check username exists

CodeIgniterCheckUsername.php

//---------------------------------
// EMAIL EXISTS (true or false)
//---------------------------------
private function email_exists($email)
{
	$this->db->where('email', $email);
	$query = $this->db->get('users');
	if( $query->num_rows() > 0 ){ return TRUE; } else { return FALSE; }
}

//---------------------------------
// AJAX REQUEST, IF EMAIL EXISTS
//---------------------------------
function register_email_exists()
{
	if (array_key_exists('email',$_POST)) {
		if ( $this->email_exists($this->input->post('email')) == TRUE ) {
			echo json_encode(FALSE);
		} else {
			echo json_encode(TRUE);
		}
	}
}