Best practices on JavaScript modularity: when to use named exports, how to group code and what to avoid. Check JavaScript Module Best Practices.
Understanding the proxy pattern and adding that to your toolbox is super useful. In the past I have used proxies for multiple purposes (logging, performance, caching results). Learn more about JavaScript proxy in JavaScript Proxy Object Explained post.
Have you read “JavaScript: the good parts”? Check this article on The Magic Behind JavaScript Sintaxis Shortcuts to learn more about not so good practices (well except maybe ternary operator)
Let’s finish with some js basics. Here’s an article that quickly explains how to declare variables: JavaScript Variables: var and let and const. I tend to agree with the statements made in the article, const is your ally but there is one caveat that you need to understand. A value declared in a const cannot be mutated, but objects or arrays are always mutable constructs, so while you can declare an object or an array as a const it is possible to mutate its properties/items. It only won’t be posible to assign something else to that const!
Juan Manuel Allo Ron