iframe + exitFullscreen = 报错？Failed to execute 'exitFullscreen' on 'Document'

当在页面中使用iframe内嵌页面时，当内嵌页面输入无效的地址时会不会报错，只有内嵌页面有页面可以正常展示时，为iframe增添全屏和退出全屏的按钮，退出全屏时会报错：``` Failed to execute 'exitFullscreen' on 'Document': Document not active

    exitFullScreen() {
      let exitFull = null;
      if (document.fullscreenElement) {
        if (document.exitFullscreen) {
          exitFull = document.exitFullscreen();
        } else if (document.mozCancelFullScreen) {
          exitFull = document.mozCancelFullScreen();
        } else if (document.webkitCancelFullScreen) {
          exitFull = document.webkitCancelFullScreen();
        }
        exitFull && exitFull.then(() => {
        console.log('退出全屏')

          this.$emit('input', false);
        });
      }
    },
   特咨询各位大佬，这啥问题呀