clearCurrentDragSourceNode in HTML5BackendImpl.ts report an error

[SnowsofKilimanjaro]

I want to know why the setTimeout method is used directly in the setCurrentDragSourceNode function, but clearCurrentDragSourceNode uses this.window?.clearTimeout(this.mouseMoveTimeoutTimer || undefined). In this way, if the value of this.window is not Window but a dom element , the dom element does not have a clearTimeout method, then this sentence will report an error