How do I embed JavaScript code into a Google Sites page?

Question

I have a Google Sites page. How can I embed JavaScript code in it, without implementing a gadget and adding JavaScript code in that?

Answer 1

Google has updated their mechanism for embedding HTML and Javascript.

See https://gsuiteupdates.googleblog.com/2017/12/embed-html-and-javascript-in-new-google-sites.html.

It is still sandboxed in an iframe with the limitations mentioned in @Serge Populov's answer.