Personally https://www.w3schools.com/js/default.aspjsbin.com
Javascript.info and https://www.tutorialspoint.com/javascript/index.htm are awesome
sites for learning Javascript!
For practice, go to https://www.w3schools.com/js/tryit.asp?filename=tryjs_myfirst and
copy/paste this and you're good to go:
<!DOCTYPE HTML>
<html lang="en">
<head>
<title>Javascript stuff</title>
<meta charset="UTF-8">
<style>
/* Styling */
</style>
</head>
<body>
<!-- Your HTML -->
<!-- JQuery <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.6.0/jquery.min.js" integrity="sha512-894YE6QWD5I59HgZOGReFYm4dnWc1Qt5NtvYSaNcOP+u1T9qYdvdihz0PPSiiqn/+/3e7Jo4EaG7TubfWGUrMQ==" crossorigin="anonymous" referrerpolicy="no-referrer"></script> -->
<script>
// THE SWEET STUFF
</script>
</body>
</html>
Personnally https://www.w3schools.com/js/js_exercises.asp