Is there some function in javascript or React.js to tell if a user tries to access an existing page through the URL bar?
In plain javascript:
window.history
How do I modify the URL without reloading the page?
In React, use should use React Router along with useHistory hook :
https://reactrouter.com/web/guides/quick-start
You can use useHistory hook:
import {useHistory} from “react-router-dom”
Then :
const {location} = useHistory()
console.log(location.pathname)