You study the Javascript basics, you know how to work with events, functions and objects. You created your a Todo App, a Weather, Map App or something similar. Maybe you even have work on a real life project.
Still, you don’t feel strong and competent with Javascript, not enough to understand most of what is happening while you write a program.

Here are some tips and resources that helped me get fully confident when writing JS code.

Get strong with JS fundamentals

If you want to have a full understanding of what you are doing while writing Javascript, you need to go back to the fundamental of it, read again and go even deeper with it.
While learning our brain has a certain capacity of understanding. When you learn some concept the first time, you could understand till a certain point. Now, after some practice, your brain is ready to go deeper.
In particular be sure you fully understand:

• Scope — I recommend Scope book from the series “ You don’t know JS”
• This / prototype — Again, from “You don’t know JS” series: check this book
• Callback / Closures — same book as for the scope
• Learn about Javascript Engine
• Design Patterns like MVP — check Javascript Patterns book (be sure to get the latest version)
• Functional vs Objects
• Algorithms — even if you don’t need to write them as a frontend developer, knowing them will help you change your way of thinking and tackle problems. If you are not a very math-oriented person, I recommend you this simple and fun book: Grokking Algorithms

Coding Interview preparation

I discovered the world of “interview preparation” questions while I was preparing for interviews and then I kept practicing and learning even without interviews coming up.
There are lots of resources online about this topic, mostly questions or code challenges and they usually deal with fundamental Javascript or even general programming topics.
I would suggest to taking some of the questions as starting points to learn more about a certain topic.

• https://github.com/learning-zone/javascript-interview-questions
• https://www.toptal.com/javascript/interview-questions
• https://www.fullstack.cafe/blog/javascript-code-interview-questions

I would suggest you check resources that have 10 to 30/40 questions to focus on the most important and not feel overwhelmed.

Code workouts

I like to call code workouts the code challenges that aim to solve small pieces of logic.
Getting stronger on these small tasks will allow you to be more confident and faster when writing this code in a bigger project.

Here are some workouts for Javascript developers:

• WesBos 30 days of JS
• Codewars Kata
• Array methods (map/find/filter/reduce) — If you feel confident solving a problem with one method, try to solve it with another one.
• Manipulate data — build complex data samples with objects and array’s of object and play around with them. Display lists, change orders, filter informations, …
• Manipulate strings

If you still struggle to understand the assignment or start a new project from scratch, you might need to improve your problem-solving skills.
Check these recommendations on how to think like a programmer.

Remember: Give yourself time. It takes time to learn all of the above. Don’t try to learn everything in a week or month, take it as a constant learning journey.
You are on the good path!