You can add getData method in your js file:
getData: function() {
return {
'method': "methodcode",
'additional_data': {
'customfield1': $('#'+this.getCode()+'_customfield1').val(),
'customfield2': $('#'+this.getCode()+'_customfield2').val(),
}
};
},
then you can get these fields in additional data
param in your payment model:
namespace Namespace\ModuleName\Model;
class Payment extends \Magento\Payment\Model\Method\Cc
{
public function assignData()
{
$post = $data->getData()['additional_data'];
// write your custom code
}
}