I tried to upload a banner with javascript on a web page provided by a free web host. I could not see the banner on the page. Does it mean that some free web hosts accept only HTML versions? Or should I have tried better?
I suspect you’ll be much better off reading the ToS of the site you’re using, to get a clear answer, rather than asking us to speculate about what might be happening. 
It depends, if the code is incorrect it might not display or it could be the service as suggested. I would recommend you use a service like jsfiddle to see if the code executes or runs correctly there. That way you will know.