_gift_checkout.js

// do some stuff with the breadcrumbs
$('ol.progress-steps > .current-first')
  .after("<a href='#' class='bill_breadcrumb'><li class='completed-first'><span>Billing</span></li></a>")
  .wrap("<a href='#' class='ship_breadcrumb'></a>")
$('input.submit_promo').on('click', function(e){
    e.preventDefault();
    if ($('#order_bill_address_attributes_firstname').val().length == 0) {
      address.toggle();
      address.toggle_bill_crumb();
      address.push();
    } else {
      $(this).click();
    }
});
$('.bill_breadcrumb').on('click', function(e){
  e.preventDefault();
  address.bill_crumb();
});
$('.ship_breadcrumb').on('click', function(e){
  e.preventDefault();
  address.ship_crumb();
});

var address = {
  toggle: function() {
    $('fieldset#shipping').toggle();
    $('fieldset#gift-billing').toggle();
  },
  toggle_bill_crumb: function() {
    $('.bill_breadcrumb > li').toggleClass('current-first').toggleClass('completed-first');
  },
  toggle_ship_crumb: function() {
    $('.ship_breadcrumb > li').toggleClass('current-first').toggleClass('completed-first');
  },
  push: function() {
    history.pushState(null, null, window.location + '#billing');
    this.pop_listener(true);
  },
  pop_listener: function(truthy) {
    var self = this;
    if (truthy) {
      window.addEventListener('popstate', function(e) {
        self.toggle();
      });
    } else {
      window.removeEventListener('popstate');
    }
  },
  bill_crumb: function() {
    if ($('.ship_breadcrumb > li').hasClass('current-first')) {
      this.push();
      this.toggle();
      this.toggle_bill_crumb();
      this.toggle_ship_crumb();
    }
  },
  ship_crumb: function() {
    if ($('.bill_breadcrumb > li').hasClass('current-first')) {
      window.history.back();
      this.toggle_bill_crumb();
      this.toggle_ship_crumb();
    }
  }
}