A Junior basically has no skills, so it's really about who they are and how they will grow while under you.
The first thing I do is suggest a code test. If they tell me they don't do code tests and think they are stupid I would probably hire them on the spot, as code tests are stupid and meaningless and tell you nothing and waste everyone's time.
After I tell them that was a joke and that code tests are stupid, I look for how they act as people. I give them a lot of room to brag or otherwise hang themselves by talking about things they don't understand all the way. If they make things up or their knowledge is way off, I end the interview early.
If they clearly know their skills and where their knowledge ends, I ask them what they are interested in. If they're interested in learning, and especially if they are excited about learning, I hire them.
If they're interested in helping others, and especially if they are excited about helping others, I also hire them.
If they're assertive (not cocky, not selfish, not boastful, but assertive), I also tend to hire them.
If they don't use stop-think sentences (like "the buck stops here", or "that's when the rubber hits the road"), or use them seldomly, it shows they go out of their way to think for themselves and that also gets them brownie points.
If there is an opportunity for me to show them they are wrong about something and they take it well, they also get brownie points. Blame isn't real and being wrong is exciting and should be celebrated, if they know this then they will go very far very fast.
If they don't trip any of the above flags, they go into the maybe pile or I consider other skills or personality traits, but they usually trip at least a few of the above flags.
We don't usually talk about code.
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