It heavily depends on the company and area I'd say. At my company, an IT-Consultancy in Germany, the junior-position-baseline is a solid understanding of HTML

It heavily depends on the company and area I'd say. At my company, an IT-Consultancy in Germany, the junior-position-baseline is a solid understanding of HTML and CSS, and at least a basic grasp of Javascript. For mid-level-positions I expect "fluency" in all of those areas, plus a good knowledge of standard-tools and accessibility. I also look for a good foundation in either design or CS, depending on the interviewees background. The interview is the same for every level, though we look for different things of course. We ask the applicants to set up a basic front-end-file-structure and to start coding a design we created specifically for interviews. During that we ask them to think aloud and talk about the reasons they do things the way they do. The second exercise is a palindrome-function in JS (or on the whiteboard for juniors). They seem like simple tasks, but you wouldn't believe how many interviews we had where the person couldn't even code an img-tag from mind. I understand that at Valley-Companies/Start-Ups, Frontend-Development includes many more advanced topics than in our case.