How to set charset="utf-8" in the javascript file itself

I am trying to set charset="utf-8" inside the javascript file itself, not in the script tag,I know that I can do this:

<script type="text/javascript" charset="UTF-8" src="xyz.js"></script>

But unfortunately, this solution needs me to do the same step with hundreds of websites which are using the same script. so I am trying to set the charset in the javascript file itself. Is this possible?

thanks