If you don't add it, it seems that the problem only occurs in ie6. It has happened: changing the image address, the image disappeared, loading the style, but the style file is gone. Just like interrupting the download of resources, the correct explanation is that when using the A element as a button under IE6, you must remember to call preventDefault() in the onclick event. IE6 will forcefully close the currently active HTTP connection, resulting in the request being Other resources or scripts are not loading properly. But if the resource has been cached, there will be no such problem