I started my first job as a junior JS developer a month ago, and I'm quite overwhelmed with all the things I don't know. I feel like the knowledge gap is vast between my colleagues and me.

So what's the best advice you can give for me and how I can keep improving myself. I used to take many online courses before I started, but now my time is limited, and can't watch as much as before :(

Stop watching and start coding.

All of this was invented by humans for humans. If they could've invented it, you can learn it. Just give it time and go step by step 🙂

Just keep going!
The first couple of months will be a little overwhelming wherever you work.
If you enjoy it, you’ll learn super quick, within three months of my junior position I was starting to get more comfortable and had a wealth of knowledge. But I still feel there’s so much to learn!
If you get some spare time read up on some of the technologies you use to get ahead of the game.

You may face a situation where you are reluctant to jump into hands-on thinking, you do not have adequate knowledge and ground... Just break that jinx.. you will see a big transformation in approach... Learn on the job(aka, on the code)...utilize the learning in your next pass of struggle..

I have been doing that ever since with all the new things I explored...And..Loving it..

As others have said, the best thing to do is do what you're asked. If you don't know something, find out how. (Your search engine of choice is your friend.) The human brain attaches more importance to things acquired during active learning, so learning for actual projects tends to stick better and get retrieved more easily. It also has the advantage of self-selecting the stuff you'll use the most for you.

There will always be some one smarter than you.

Dont hesitate to ask questions. Dont hesitate to bug people for questions
Show that you want to learn.

But， be sure that you tried to investigate yourself first. formulate your issue correctly and explain what avenues you have tested (all this as accurately and breifly as possible)， and what direction you think it might be going.

Also make a template sentence:

“hi， my problem is this ... I expect ... But i get ... I tested a， b and c but wihtout success.”

Find a good coder and make him/her your code sis/bro. Find the coder that is strict! Thought process is probably the most important skill.

Also get on irc freenode. You have some great rooms with some brilliant people who are online all the time and answer questions all the time. Sometimes i wonder if they are human. I use kiwiirc in the browser or when linux use hexchat.

Learn to read the documentation.

Stay humble. You’ll most likely have this feeling throughout your career, even as you progress and get better. For every new thing you learn there’s most likely a leaf attached to it that opens up to yet another thing you didn’t know.
This is a good thing, and a big part of why developing is fun.
Stay humble, stay hungry.