it will be good if there's and button field in the form body , 

it can help in the type of form where an algorithm has to ran or a calculation has to be done on user input more often.

like in quote calculator form I am developing , I use decision field  right now , which seems inappropriate , since whenever user click calculate, after performing the calculation I have to uncheck  the field via script to make it clickable once again due to which it runs the user input script once again.

it would be better if there's and button field , which we can be include in both statefull & stateless form ( inside the Form body ) which will not trigger the form to submit ( unlike stateless form ), it will just trigger the script on user input. so that taking & changing input -> triggering the calculation can be shown more appropriately.

and this feature has been asked by many of my clients.