How to read formControlRange Value after pressing a button

[jeroen.rottink]

I never used the combination from HiddenFields with controls like Alexandre suggested. Didn't get that working either.
Following is what I use and works.

Code:

// btnCheck2.ScriptEvents.onClick
document.getElementById("HIDDEN_signature").value = "something";
AddChangedControl("HIDDEN_signature");

procedure TIWForm1.IWAppFormCreate(Sender: TObject);
begin
  HiddenFields.AddPair('signature', '');
end;

procedure TIWForm1.btnCheck2AsyncClick(Sender: TObject; EventParams: TStringList);
var Signature: string;
begin
  Signature := HiddenFields.Values['signature'];
  if not Signature.IsEmpty
  then WebApplication.ShowNotification('Signature received')
  else WebApplication.ShowNotification('No signature...');
end;