How to declare character encoding in an INDIVIDUAL JS file?

We can declare the character encoding in an INDIVIDUAL CSS file by codes below:

@charset "UTF-8";

My question is:

How to declare character encoding in an INDIVIDUAL JS file?

If I send a JS file to my friend, I hope he (she) can understand this JS file's character encoding from codes themselves when he (she) starts to browse or edit this JS file.

Thank you!