JS 判斷手機目前是橫屏還是豎屏

function rotate() {

      if (window.orientation == 180 || window.orientation == 0) {
      alert('豎屏')
      }
      if (window.orientation == 90 || window.orientation == -90) {
      alert('橫屏')
      }
    }
    window.addEventListener("load", rotate, false);
    window.addEventListener("onorientationchange" in window ? "orientationchange" : "resize", rotate, false);