The random URL works, but it's kind of a hack. HTTP has solutions built in that should work. Try using the solution indicated here. Basically, set the headers:
"Pragma": "no-cache",
"Cache-Control": "no-store, no-cache, must-revalidate, post-check=0, pre-check=0",
"Expires": 0,
"Last-Modified": new Date(0), // January 1, 1970
"If-Modified-Since": new Date(0)
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