How do you learn "on the job"?

Be extremely comfortable looking dumb.

That's it. That's the 1 concept you need to remember. If you truly internalize this, you will naturally do all the corresponding action items that I've seen so many newbie engineers mess up:

1. Aggressively probing for feedback
2. Asking questions when you're stuck
3. Biasing towards action (usually coding) instead of trying to get things perfect on the 1st try reading 500+ pages of documentation
4. Treating others with respect and communicating gracefully as if you're happy looking dumb, it makes 0 sense to chastise others for looking dumb

Scope down what you're learning. This is what I call the "Taro Expertise Theory" 😅

Taro Expertise Theory: You can become more knowledgeable than anyone:

• Within a group of people P (e.g. the team of 10)

• Within a certain domain D (e.g. the build system)

• Within a certain time T (e.g. a week)

This theory removes the question of “feasibility” around being an expert. You just need to vary these parameters in order to become an expert.

For example, as an intern, maybe you can learn more about the JavaScript linting rules and make improvements for your team. You've quickly become the "expert" for that narrow area, and that can be used to build trust and then expand your expertise.

Learn more in this section of the onboarding course: The Common Misconception With Help

We know onboarding is already tough - meeting new people, understanding new codebase, etc. In the first few weeks especially, how do you manage so many things?

There are definitely a lot of different priorities to juggle, but your team will be more forgiving to new hires, so you do have some leeway. That being said, you should really strive to put in the extra work at the beginning to ramp up as quickly as possible. I also see that you are an intern, so they'll probably be even more forgiving :)

Let's say I don't have ANY frontend experience in the past, but somehow get hired at a FAANG as a frontend dev.

The good thing is that you can do some supplementary studying to get a better grasp on frontend technologies. I recommend Frontend Masters to learn more about web technologies. Focus on the courses that apply to the tech stack that you're working on.