TouchList：length 属性

const target = document.getElementById("target");

target.addEventListener(
  "touchstart",
  (ev) => {
    // If this touchstart event started on element target,
    // set touch to the first item in the targetTouches list;
    // otherwise set touch to the first item in the touches list
    const touch =
      ev.targetTouches.length >= 1
        ? ev.targetTouches.item(0)
        : ev.touches.item(0);
  },
  false,
);