Can you show me the errors?
First you need to find out weather the problem is on your end or on itch.io. Basically dose it run on your computer at all?
Since you haven't corrected me I will continue asuming that you work with unity. Is your original webgl build file still on your computer? You shouldn't be downloading it from itch.io every time you want to test it. Just open the index.html file in a browser.
Please give me the exact error massage. "Some java script failed" will only get you the answer "then fix it".