Alternative to RegisterOnSubmitFunction(…);

First of all , greetings to all .
I opened this topic to see if someone can support me in the following issue .
I've been using for several years a system which I program processes, which I have no access to the code. On the client side allows me to create forms in which I can use javascript and the system adds the Submit button to the form, which I have no control to.
Today I am migrating to a new version of the system and I have to develop some forms. A function widely used to perform…
Alternative to RegisterOnSubmitFunction(…);

See original post by mvelazquez