Javascript inside a Bonita Designer form

Hi

I have a observation.
The Scenario is that I have a custom Living app page. There I have 2 separate Lists of type multiple.
My contract is a Single list of Type multiple.

What i am doing here is Adding the values of the 2 lists together and sending it to my contract.
I am using JavaScript to perform this.
In side the custome page , it works fine.

Now along the process , I need to do the same inside the process.
This time its a Bonita portal form . I am using the same JavaScript code in the formOutput section but its does not respond . I am getting a contract violation error . If I remove the JavaScript and simple Add it like
Contract = $data.formInput.List1 then it works fine.

Is there any restriction inside forms to use the same JavaScript that we can use inside Living app page .

Also is there any specific ways to implement Javascript in forms using any other script ?