HTML5 DragNDrop - Drop事件永远不会触发

I'm trying to implement a drag'n'drop upload input for a web app. Detecting drag start and end and appropriate drop target styling works flawlessly, though as soon as I drop an image file on the target, it opens in the browser. I know this has been asked pretty often on SO, but I couldn't find a solution anywhere yet. I'm trying to implement a drag'n'drop upload in