Realtime fetching from normal MySQL DB | Realtime data in PHP MySQL 

You can improve this, create a different table 'watcher' just look at the record in the watcher and if record change fetch data from real table. Always update the watcher after modify real data table like adding, updating, deleting. You can use time stamp to use in watcher.

it takes too long to load, and it gives VM271:1 Uncaught (in promise) SyntaxError: "[object Object]" is not valid JSON at JSON.parse ()

That's a very basic functionality, just create a function doing all stuff and run that function inside on message event.

and it will sending multiple data as time goes by

No, not a such heavy as you think, and it doesn't send data each it just check the data if available them send

@@hacodes my codes sometimes it keep repeating it self even though it's already executed as time goes by, is it because the read time get more slower because of the infinite loop?

Loop continue running when connected with client request, as request abort server processing stops for that request. And loop is just continue to check new data, if new data no available, then show nothing but keep running. This method still better that keep requesting from client side continuously.

@@hacodes what if there is so many table and data, is it going to be slow?