Running JavaScript:

We can run JS on the browser's console by which we will have access to the page we are on.

Also we can run it in a script tag:

<script>
console.log('Heyyy');
</script>

Always try to have your script tag before the closing body tag, because we can access the HTML elements written above the script tag as they are above the JS.

Also, we can run JS in another file using script tag with src attribute:

<script src='relative path to js file'></script>

Also we can run it via Node.js - instead of running in the context of a website we run it in an actual machine. In console, run: node file.js