triggere.html

<script>
AFRAME.registerComponent("trigger-listener", {
  init: function () {
    var el = this.el;
    el.addEventListener("triggerdown", function (evt) {
      document.getElementById("ball").emit("throw");
    });
  },
});
</script>

<a-entity
  id="primaryHand"
  oculus-touch-controls="hand: right"
  trigger-listener>
</a-entity>