What you should already know
What we’d really like (in order of importance)
How will you work?
We’re moving fast, and as a frontend engineer, you will have a lot of freedom and autonomy to work in the way you prefer. That also includes responsibility and being comfortable to make decisions and solve problems in an efficient manner.
While a good knowledge of JS is necessary, knowing all the ins & outs and gotchas of CSS/SASS & HTML is a must.
You should see HTML & CSS as powerful languages which you feel fully confident using, not as side languages you sometimes use and get bored if you use them too much.
Your level of CSS & HTML and what you have done with it matters much more than JS in this interview.