What is for?

Question

I wonder what this tag in script stands for <!--> //--> I've noticed it in some usage of javascript, but not always.
Is this necessary or can you just keep it out and what is it's major use?

Answer 1

Before javascript existed, browsers did not know what <script> meant. The tag didn't exist yet. So those browsers would attempt to output the javascript directly! To work around that, we would comment out the javascript with <!-- html comments -->. However, the ending html comment --> is a javascript syntax error, so we have to comment that out with // javascript comments. Nowadays, browsers are smarter and can handle these edge cases.

Answer 2

Those are to create comments in XML and HTML.

<!-- this will not show -->
But this will.

They are included in scripts to hide the code from browsers (technically, this can be a number of different devices, but I'm using "browser" for short) which don't allow for JavaScript.

<script><!--
doSomethingJavaScripty();
// -->
</script>

This means the browser without JavaScript will not accidentally display doSomethingJavaScripty();. It is often paired with a noscript tag (which a browser that supports JS will safely ignore).

This is technically optional. Often times it is a relic of a now-forgotten past, but it is conceivable that it might be useful at some point. It might happen, for example, that you eventually want a service to read and parse your webpage. In such a case, adherence to good practice will prove beneficial. But, even in that circumstance, it has become more common (thankfully) to move to something called "unobtrusive JavaScript."

Answer 3

its used when developers wants to be on safe side, that if browser doesnot support javascript then the code will not be rendered as text, it will become comment