Sometimes you just want to put a small snippet of code into another page. A small “injector” script like this pasted into the F12 developer tools can do the trick fast.
var s = document.createElement("script");
s.type = "text/javascript"; s.async = true;
s.src="https://gully.org/uxb/helloworld.js";
var h = document.getElementsByTagName("head")[0];
h.appendChild(s);
small snippet injector
code