ReactJS app not immediately running when mobile browser visits website, and takes 3 seconds for the code to start running

I am using ReactJS. When I visit the website using my phone, it seems to display instantly (maybe a cached version?) and only after 3 seconds does the website actually begin to run the javascript code that pulls data from a database.

Is there a way to prevent this latency? I.e. once user visits reactjs website, it should immediately start running the javascript.

I suspect it might be a caching issue, as the website seems to load instantly when I hit enter on my phone, and it takes some time to actually download the index.js and all from my webserver. But at the same time I’m not sure, is there a way to test this too?

Thanks, and cheers for the help.