In order to prevent someone from uploading specific file types, you would need to list all the file types you will accept. If your are using the
mimetypes parameter this becomes easier because you can use wildcards like
"image/*", to say you will accept all image filetypes. With the
extensions parameter, you would need to list them all out like [".jpg",".gif",".png", etc..].
One note of caution when providing a long list of extensions or mimetypes is that these get appended to the Filestack dialog URL.
This is important because some browsers have a limit on how many characters are allowed to be in a URL. Internet Explorer, for example, has a limit of 2,083 characters for URLs. So if you put a really long list of extensions or mimetypes, you could go over this limit and then the dialog will fail to load because the URL will be invalid.
In v3 however, it is possible to provide both extensions and mimetypes that you want to accept, and it is also possible to reject certain filetypes by defining your own custom functions.
Someone from our team will get back to you shortly.