Prior conversations have suggested that this sort of validation would probably best be done in APEX…

https://community.skuid.com/t/file-upload-type

Temporary fixed it with javascript.

For anyone interested:

$('INPUT[type="file"]').change(function (event) { var ext = this.value.match(/.(.+)$/)[1]; switch (ext) { case 'jpg': case 'jpeg': case 'png': case 'gif': break; default: alert('This Filetype is not supported.'); this.value = ''; window.stop(); } });<br>

Sweet!  Good work Thimo…

Hi Thimo, I have similar requirement. How can we call this snippet from file upload button?