javascript - 如何使用javascript或react检查touchevent是否存在？

Question

我想摆脱 safari 浏览器上的错误“referenceError:找不到变量 TouchEvent”。我的代码如下，

function copy_mouse_event(event) {
    const event_init = {
    // EventInit
    bubbles: event.bubbles,
    eventPhase: event.eventPhase,

    // UIEventInit
    detail: event.detail,
    view: event.view,

    // EventModifierInit
    altKey: event.altKey,
    ctrlKey: event.ctrlKey
  };

  // initialise MouseEvent data which is shared by wheel, mouse and pointer events
  let mouse_event_init = {};
  if (event instanceof MouseEvent) {
      mouse_event_init = {
          ...event_init,
          button: event.button,
          buttons: event.buttons,
          clientX: event.clientX,
          clientY: event.clientY,
          relatedTarget: event.relatedTarget,
          screenX: event.screenX,
          screenY: event.screenY
      };

      if (event instanceof WheelEvent) {
          const wheel_event_init = {
              ...mouse_event_init,
              deltaMode: event.deltaMode,
              deltaX: event.deltaX,
              deltaY: event.deltaY,
              deltaZ: event.deltaZ,
              wheelDelta: event.wheelDelta,
              wheelDeltaX: event.wheelDeltaX,
              wheelDeltaY: event.wheelDeltaY
          };
          return new WheelEvent(event.type, wheel_event_init);
      }
  }

  // try the modern pointer event first, then mouse and touch events
  if (event instanceof PointerEvent) {
      const pointer_event_init = {
          ...mouse_event_init,
          pointerId: event.pointerId,
          width: event.width,
          height: event.height,
      };
      return new PointerEvent(event.type, pointer_event_init);
  } else if (event instanceof MouseEvent) {
      return new MouseEvent(event.type, mouse_event_init);
  } else if (event instanceof TouchEvent) {
     //error occurs here only on safari
     const touch_event_init = {
         ...event_init,
         changedTouches: event.changedTouches,
         targetTouches: event.targetTouches,
         touches: event.touches
     };
     return new TouchEvent(event.type, touch_event_init);
 }
}

由于 safari 浏览器不支持触摸事件，我想通过检查触摸事件是否存在来修复。我如何检查 touchevent 是否存在。有人可以帮我解决这个问题吗？谢谢。

Answer 1

要检查 TouchEvent 是否存在，您可以执行以下操作:

if ('TouchEvent' in window) {
   ...
}

仅检查 TouchEvent，如 if (TouchEvent ...) 不起作用，就好像它未定义一样，您将收到运行时错误。执行此操作的有效方法是:

 if (window.TouchEvent) {
     ...
 }

编辑:如果你想使用typeof，你可以这样做:

if (typeof TouchEvent !== 'undefined') {
    ...
}

使用您喜欢的方法，因为两者都有效。

希望这有帮助。