Below are some things I look out for when interviewing junior developers. It's obviously not a comprehensive list, but hopefully gives you a little insight into what some interviewers are looking for.
For what it's worth, I'm based in the UK.
Don't lie in your interview. If you don't know something, be honest. If you're confident you could learn it quickly, say so, and explain why:
By admitting you don't understand something, it adds credibility to everything you've said before.
Tell me about your side projects! If you've made a side-project you're super proud of, but are a bit wary of sharing because it's geeky, tell me anyway! It doesn't matter if I understand the reference, it shows a passion for coding.
If you're passionate I care less about what you know. I can teach you to code, but I can't teach you enthusiasm.
An interview is a 2-way street. I'm interviewing you to see if you're the right candidate for the role just as much as you're interviewing me and the company to make sure we're a good fit for you. If you accept the role you'll be spending nearly 8 hours a day inside the company's walls - make sure you're happy with that!
Also ask about the team you'll be joining. How big is it? How supported will you be? Are there frequent social events?
Asking questions also rings true for any "take home" problem you might be given. If you don't understand the problem, ask; just don't ask how for the solution. For example, don't ask: "How do I order an array?", but rather "Would you like the array ordered by name, or total?").
This shows a keenness to understand the problem correctly, and also shows off a little of your knowledge because you know arrays can be ordered in different ways.
This is true for any level of interview to be fair, but for God's sake do your research before you go to an interview. I won't be trying to trip you up, or grilling you on what our last product launch was, but I'll know straight away if you haven't even looked at our website.
One thing I like to do if I'm being interviewed is find one cool project the company has done recently and bring it up in my interview.