Research on the Input button function of JavaScript type File_Form special effects

For example, http://www.youku.com/v1.0.0326/v/swf/up.swf
This is Youku’s video upload option, which uses FLASH to prevent non-video files from being displayed.
FLASH to this effect is generally as described here

So for the <input type="File"> in our webpage, can we also implement pop-up windows to limit file types?
The current solution can only be to remind users that the format of the uploaded file is incorrect through monitoring
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If you need to introduce external Js, you need to refresh to execute
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<script> function check(){ var filepath=path.value filepath=filepath.substring(filepath.lastIndexOf('.')+1,filepath.length) if(filepath != 'jpg' && filepath != 'gif') alert("只能上传JPG或GIF格式的图片") } </script>However, this effect obviously does not FLASH has a good user experience. It is necessary to pay attention to this type of FLASH upload. <script> function ck(obj){if(obj.value.length>0){ var af="jpg,gif,png,zip,rar,txt,htm"; if(eval("with(obj.value)if(!/"+af.split(",").join("|")+"/ig.test(substring(lastIndexOf('.')+1,length)))1;")){alert("Allowed file types:\n"+af);obj.createTextRange().execCommand('delete')}; }} </script>