At the beginning of my career I didn’t always enjoy front end development because no matter where you turned Javascript was always lurking, and I didn’t really like it. The dynamic nature of Javascript always made me uneasy because I had been so used to Java.
Thankfully the game has really changed, especially because of a library like Typescript coming in and doing its best to provide type safety in Javascript, Google thought it was so good they actually bundled it with Angular, formally AngularJS.
I purposely used the words doing its best because Typescript only has so much power in Javascript land. It is very important to remember that Typescript is really just syntactic sugar for development, and once your code is transformed to a production ready state for the browser, Typescript has no power.
I would forgive someone reading this and thinking, well why is it so important to understand this and why can I not just let my tools do their work. Two reasons…
The most obvious reason is just the benefit of comprehension, knowing this and other lower level dynamics of Javascript will improve your over all understanding of the language and make you more versatile.
The second reason is maybe not so obvious, but it is basically knowing this to ensure you don’t misuse Typescript. The worst misuse I have ever witnessed was in a React repo I found linked on a dev forum, the developer had a page with a form that required user input validation, and they had attempted to use Typescript to enforce input. This would never result in actual working client side validation because as stated before – at runtime the browser does not actually care about any type safety that was enforced by Typescript during development.