Q:

Is button.app-submit a valid jquery selector?

Is $('button.app-submit') a valid jQuery selector? If so, can you please explain which part is the class or id and how the html would look like.

A:

It is valid selector and it does not have id component. With this selector, you are telling that among all buttons select only the ones with .app-submit class.
An example for id selector would be: $('#MyButtonId')

