• 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