halloween.js / Google Tag Manager

Add Halloween effects to Google Tag Manager

If the site already runs Google Tag Manager, you can switch the effects on and off from a tag without touching the site code.

Steps

In your container open Tags → New and choose Custom HTML as the tag type.
Paste the snippet below into the HTML field.
Set the trigger to All Pages, name the tag, and save.
Preview the container, then Submit and publish the new version.

The snippet

One paste, no other files. It loads halloween.js 1.0.3 from jsDelivr and turns on webs in two corners, blinking eyes, flying witches, a dropping spider and a rising tombstone.

<script src="https://cdn.jsdelivr.net/npm/halloween.js@1.0.3/dist/halloween.iife.js"></script>
<script>
(function () {
  function apply() {
    document.body.classList.add("halloween", "halloween-screen-left-top", "halloween-screen-right-bottom", "halloween-eyes", "halloween-witches", "halloween-spider-drop", "halloween-tombstones");
  }
  if (document.readyState === "loading") {
    document.addEventListener("DOMContentLoaded", apply);
  } else {
    apply();
  }
})();
</script>

Make it yours

Pick corners, effects, intensity, color and season dates in the playground and open the Paste-only tab. It produces this same snippet, library line included, with your choices.

Good to know

The effects only appear in a window around Halloween, 18 October to 2 November by default. Change the dates in the playground to see them on another day.
Ambient effects stop when a visitor has reduced motion turned on. The screen-corner webs stay.
The effects sit in a fixed layer and never shift your page layout.
Pause the tag when the season ends if you want the effects off earlier than the built-in season window.
Nothing showing? Reload without cache, then check that the snippet is on the live site and that no content blocker is stripping it.

Other platforms

All options on the halloween.js home page, full documentation on GitHub.