How to use "bold" inside a variable string

const error = "You are not authorized to work on this form for "+ data.employee.username +".<br>"Ask your admin for access."

This shows perfectly like this:

You are not authorized to work on this form for <username>.
Ask your admin for access.

so the <br> command is recognized. But when adding <b> to make the username bold it doesn't work. I tried putting it inside and outside the quotation marks and all, no luck.

Please assist, thank you!