Argthtjtr

After working with my boss at a previous job he's decided to start a contracting firm and I'm in the first handful of people to help get things started. It's been a few months and now we're looking to expand and hire a more junior developer.

I've helped my boss hire knowledgeable senior level people that I was going to work directly with. It was easier to ask hard questions and if they had a correct answer then I could believe they were good for the job. If I ask a senior person hard questions that they don't know the answer to, I start to have a feeling it may not be a good fit.

Trying to come up with questions for a junior level has me second guessing how to receive their answer. If I ask a junior person easier questions and they don't have an answer, is it because I asked a slightly too hard question for a junior? Should they know this answer? If they got it right, did I ask too easy a question? In theory it makes sense to ask them some technical questions but also some "are you capable of learning what you need to know in order to do your job" kind of questions but that's turning out to be hard in practice.

How can I ask the right questions and set my own expectations properly for interviewing a junior candidate?

As a slight frame challenge to your question, you need to get some clarity on what the role requires and then ask questions specific to that. In other words, I have the feeling that your real problem is that you don't have a clear idea of what skills you want in this person. Find that out and the questions will follow.

Stop over-thinking "easy" versus "hard" questions. Write down what the person needs to be able to do and then ask them questions about what you've written down.

For a Junior, it's less about what they know, and more about who they are.

If they don't know the answer to a technical question, follow up with something like?

You said you don't know. How would you find out, and then implement it?

For the tech questions themselves, have sets of Basic, intermediate, and advanced. Climb the difficulty tree until you get an "I don't know, then ask that question above.

Ask more soft questions like:

Your senior has assigned you a task. You feel like it's beyond your abilities, what do you do?

or

How long do you see yourself staying as a junior? How would you hone your skills to be worth more to the company?

Also, keep in mind that the more junior people are also inexperienced in interviews and may blow tech questions that they know.

Go for more of the "How would you" type questions as opposed to "what is" type of questions.

most importantly

Interview for fit. Your eventual goal is to advance a junior in your company, the better a fit he is, the easier it will be to upskill him, and eventually train the next junior(s) that apply.

You can teach people more tech skills, you can't teach a jerk to be a decent person

Again, this is why you want to interview more for ability to expand and learn than for raw tech skill. If he's lacking in a few areas, you can get him up to speed. If he's going to be a disruption, nothing will cure that.

First, decide what you want the person you're hiring to actually do. Based on that, decide which skills and knowledge are important for this role. You probably want to align with your boss on those points.

Make sure that your job description and list of qualifications accurately reflect that. In terms of the job description, make sure that you accurately describe what you want the person to actually do and accomplish - describe the job, not the kind of person you're looking to hire. Once you have that, come up with your "people description" - i.e. what kind of person you're looking to hire and what your desired qualifications are. Make sure that that aligns with your job description. A good people description should describe someone who is likely to be able to do what your Job Description specifies.

A "qualified" candidate is someone who meets the requirements in your "people description."

Based on the job description and the people description, you should come up with a list of questions that'll help you know whether the person in question meets the requirements in your people description. Rank your questions in order of easiest to hardest, so that you can determine the person's skill level.

Some good questions could include, for example, reversing a string without using string.reverse (yes, some people actually get this wrong), sorting a list, or the classic FizzBuzz challenge.

It's not a great idea to put a junior on the spot in an interview. I think a far better approach is to set them a simple coding task and give them a certain amount of time to complete it. It will show their ability to learn and solve problems. You could even set this test before inviting them in for a face to face interview.

I cannot code while people watch me, it's awkward. I have always hated interviews where I'm asked to do this. Of course asking some probing questions to judge someone problem solving abilities is good but try keep it general not specific, if that makes sense?

The top answer is very good and should suffice I guess. I only want to add a small detail as a person who was interviewed for a junior position several times not so long ago. Sometimes during an interview I had an impression while being asked ('hard'?) tech questions that interviwers were rather trying to show off their knowledge than to know about mine: favourite subject seems to be little used language features or technical details (like garbage collection process) which I normally never had need to use. This is very confusing and makes junior think that he knows nothing at all.
What would be more welcome is giving a simple task with describing implementation process in common words, like creating models, ease of extending them, defining what they should do, and sometimes more important, what they shouldn't do.