The questions that almost always come up in a junior interview

There's a trap when you prepare: feeling like you have to study everything. The truth is that junior interviews revolve around a small group of topics that come up again and again. Master them and you cover most of it.

JavaScript

• let, const, and var: scope and reassignment.
• == vs === and type coercion.
• What a closure is and an example of using it.
• The event loop: why setTimeout(fn, 0) doesn't run immediately.
• map, filter, and reduce.

React

• The difference between state and props.
• What useEffect does and when it runs.
• Why lists need a key.
• What causes a re-render.

Node and Express

• What middleware is and in what order it runs.
• The most common HTTP verbs and status codes.
• How to handle errors in asynchronous routes.

Git

• merge vs rebase, in plain words.
• How to undo a commit.
• What a conflict is and how to resolve it.

How to study them

Don't read them: practice them. Each of these topics is in Interview Lab with an explanation, an example, and an exercise. Use the flashcards to review them with spaced repetition, and the What does it print? mode to check that you really understand the code.

Rule of thumb: if you can explain these topics out loud without reading, you're ready for most junior interviews.