How to get the file name in the URL using JS_javascript skills

I encountered this problem when writing a function to adapt the size of images...
Haha, I won’t go into details about the problem. I encountered another stone on the way to solve it, which is how to use JS to get the file name of the image. .
After thinking about it for a long time, I finally wrote a function...
I saved it for the first time for future use

[Ctrl A select all Note: If you need to introduce external Js, you need to refresh to execute

]
<script> var a="http://www.jb51.net/html/images/logo.gif"; var b=a.split("/"); var c=b.slice(b.length-1, b.length).toString(String).split("."); alert("取得的文件名是:" + c.slice(0, 1)); </script>