A simple shim for the HTML5 formaction attribute.

jquery.shimFormAction.coffee

# Test for formaction attribute support in Modernizer.
Modernizr.addTest 'formaction', 'formaction' of document.createElement('input')

# Shim for formaction attributes on buttons and inputs.
$.fn.shimFormAction = ->
  return this if Modernizr.formaction

  this.each ->
    $(this).find   'input,button'
           .filter '[formaction!=""][formaction]'
           .on     'click', ->
                     $this = $ this
                     $this.closest('form').attr 'action', $this.attr('formaction')
                     true

jquery.shimFormAction.js

Modernizr.addTest('formaction', 'formaction' in document.createElement('input'));

$.fn.shimFormAction = function() {
  if (Modernizr.formaction) {
    return this;
  }
  return this.each(function() {
    return $(this).find('input,button').filter('[formaction!=""][formaction]').on('click', function() {
      var $this = $(this);
      $this.closest('form').attr('action', $this.attr('formaction'));
      return true;
    });
  });
};