1. In terminal, go to the folder url_checker_js and make an environment variable FLASK_APP
    On linux or unix, it can be made with following commands.
    
        export FLASK_APP = url_checker.py

2. flask run
3. Above code will host a local server on such a link http://127.0.0.1:5000/    .Open it in your web browser and navigate the site.

Regexp checking standard solution has been taken from stackoverflow which other devs have tested.

fetch .then blocks haven't been debugged. Current setup creates 2 seconds (can be changed according to need) delay compared to last fetch. It isn't tested. If a new oninput function call overrides earlier oninput function calls, it would be optimal. If the calls pile up, it wouldn't be good code.
