why does index.html keep opening as https://www.google.com/index.html?

Im trying to check for a keyword in the url and launch an html file from javascript

here is my code:

window.setInterval(function doTheTing() {
        if (window.location.href.indexOf("keyword") > -1) {
            window.location.replace("index.html")
        }
    }, 1000)

what im trying to do is open the file when the keyword is in url, and it does work, but for some reason when i try to open index.html it opens https://www.google.com/index.html instead

*if the keyword is in the url of a youtube video than it opens as https://www.youtube.com/index.html (which isnt a real domain so it just shows an error page)

*if its from a tiktok than https://www.tiktok.com/index.html (which also returns an error page)

and so on…

how can i just open index.html?

thanks for the help