.serialize doesn't include submit buttons

[jquery@…]

It doesn't because it checks the type against rinput which is a static list of types. Which is very strange IMO.

Anyway: submit buttons with a name are part of the form value just as text inputs etc.

rinput

rinput = /^(?:color|date|datetime|datetime-local|email|hidden|month|number|password|range|search|tel|text|time|url|week)$/i,

checked in serializeArray > filter

[dmethvin]

Button values are serialized only if a button press caused the form submit.

If a form contains more than one submit button, only the activated submit button is successful. -- ​http://www.w3.org/TR/html4/interact/forms.html#h-17.13.2

When you serialize using code no button is pressed, and if a button press triggered the code you'll need to add it to the serialized input yourself.