While matt b’s answer will work, you can also use .serializeArray()
to get an array from the form data, modify it, and use jQuery.param()
to convert it to a url-encoded form. This way, jQuery handles the serialisation of your extra data for you.
var data = $(this).serializeArray(); // convert form to array
data.push({name: "NonFormValue", value: NonFormValue});
$.ajax({
type: 'POST',
url: this.action,
data: $.param(data),
});