A JS Checkout Popup for WooCommerce, asking user to NOT refresh the page while order completes. Also based on magnificPopup. Only pops up if checkout form is valid.

woocommerce-placing-order-js-popup.css

/* Styling the JS Checkout Popup for WooCommerce, asking user to NOT refresh the page while order completes. */

/* Order waiting popup */
.white-popup h3 {
  color: #3cb9f2;
}
.white-popup {
  position: relative;
  background: #FFF;
  padding: 20px;
  width: auto;
  max-width: 280px;
  margin: 20px auto;
  text-align: center;
  border-radius: 5px;
  box-shadow: 0 0 15px 0px black;
}
.white-popup-interior {
  background: #fcffe4;
  padding: 20px;
  margin: 20px auto;
  border-radius: 5px;
  border: 1px solid #d6e453;
  font-size: 16px;
}

/* Order waiting CSS animated spinner */
.loader {
  color: #4abef3;
  font-size: 7px;
  margin: 45px auto 20px;
  width: 1em;
  height: 1em;
  border-radius: 50%;
  position: relative;
  text-indent: -9999em;
  -webkit-animation: load4 1.3s infinite linear;
  animation: load4 1.3s infinite linear;
  -webkit-transform: translateZ(0);
  -ms-transform: translateZ(0);
  transform: translateZ(0);
}
@-webkit-keyframes load4 {
  0%,
  100% {
    box-shadow: 0 -3em 0 0.2em, 2em -2em 0 0em, 3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em, -2em 2em 0 -1em, -3em 0 0 -1em, -2em -2em 0 0;
  }
  12.5% {
    box-shadow: 0 -3em 0 0, 2em -2em 0 0.2em, 3em 0 0 0, 2em 2em 0 -1em, 0 3em 0 -1em, -2em 2em 0 -1em, -3em 0 0 -1em, -2em -2em 0 -1em;
  }
  25% {
    box-shadow: 0 -3em 0 -0.5em, 2em -2em 0 0, 3em 0 0 0.2em, 2em 2em 0 0, 0 3em 0 -1em, -2em 2em 0 -1em, -3em 0 0 -1em, -2em -2em 0 -1em;
  }
  37.5% {
    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em, 3em 0em 0 0, 2em 2em 0 0.2em, 0 3em 0 0em, -2em 2em 0 -1em, -3em 0em 0 -1em, -2em -2em 0 -1em;
  }
  50% {
    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em, 3em 0 0 -1em, 2em 2em 0 0em, 0 3em 0 0.2em, -2em 2em 0 0, -3em 0em 0 -1em, -2em -2em 0 -1em;
  }
  62.5% {
    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em, 3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 0, -2em 2em 0 0.2em, -3em 0 0 0, -2em -2em 0 -1em;
  }
  75% {
    box-shadow: 0em -3em 0 -1em, 2em -2em 0 -1em, 3em 0em 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em, -2em 2em 0 0, -3em 0em 0 0.2em, -2em -2em 0 0;
  }
  87.5% {
    box-shadow: 0em -3em 0 0, 2em -2em 0 -1em, 3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em, -2em 2em 0 0, -3em 0em 0 0, -2em -2em 0 0.2em;
  }
}
@keyframes load4 {
  0%,
  100% {
    box-shadow: 0 -3em 0 0.2em, 2em -2em 0 0em, 3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em, -2em 2em 0 -1em, -3em 0 0 -1em, -2em -2em 0 0;
  }
  12.5% {
    box-shadow: 0 -3em 0 0, 2em -2em 0 0.2em, 3em 0 0 0, 2em 2em 0 -1em, 0 3em 0 -1em, -2em 2em 0 -1em, -3em 0 0 -1em, -2em -2em 0 -1em;
  }
  25% {
    box-shadow: 0 -3em 0 -0.5em, 2em -2em 0 0, 3em 0 0 0.2em, 2em 2em 0 0, 0 3em 0 -1em, -2em 2em 0 -1em, -3em 0 0 -1em, -2em -2em 0 -1em;
  }
  37.5% {
    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em, 3em 0em 0 0, 2em 2em 0 0.2em, 0 3em 0 0em, -2em 2em 0 -1em, -3em 0em 0 -1em, -2em -2em 0 -1em;
  }
  50% {
    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em, 3em 0 0 -1em, 2em 2em 0 0em, 0 3em 0 0.2em, -2em 2em 0 0, -3em 0em 0 -1em, -2em -2em 0 -1em;
  }
  62.5% {
    box-shadow: 0 -3em 0 -1em, 2em -2em 0 -1em, 3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 0, -2em 2em 0 0.2em, -3em 0 0 0, -2em -2em 0 -1em;
  }
  75% {
    box-shadow: 0em -3em 0 -1em, 2em -2em 0 -1em, 3em 0em 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em, -2em 2em 0 0, -3em 0em 0 0.2em, -2em -2em 0 0;
  }
  87.5% {
    box-shadow: 0em -3em 0 0, 2em -2em 0 -1em, 3em 0 0 -1em, 2em 2em 0 -1em, 0 3em 0 -1em, -2em 2em 0 0, -3em 0em 0 0, -2em -2em 0 0.2em;
  }
}

woocommerce-placing-order-js-popup.js

// A JS Checkout Popup for WooCommerce, asking user to NOT refresh the page while order completes. Also based on magnificPopup. Only pops up if checkout form is valid.
jQuery(function()
{
  jQuery(".woocommerce-checkout").submit(function()
  {
    jQuery(this).valid() && jQuery.magnificPopup.open(
    {
      items:
      {
        src: '<div id="wait-to-complete" class="white-popup"><h3>Placing order...</h3><div class="white-popup-interior">Please don\'t try to refresh the page and wait for the confirmation.</div><div class="loader">Placing the order...</div></div>',
        type: "inline"
      },
      callbacks:
      {
        open: function()
        {
          setTimeout(function()
          {
            jQuery("form.woocommerce-checkout").magnificPopup("close")
          }, 10000) // in miliseconds
        }
      }
    })
  })
});