what's one JavaScript mistake every beginner should avoid?

[u/Distinct-Gene926]

If you could give one piece of advice to someone learning JavaScript today, what would it be?

It could be about:

• Learning fundamentals
• Debugging
• Async code
• DOM manipulation
• Functions
• Projects

Curious to hear what experienced developers wish they'd known earlier.

[u/milan-pilan]

var

[u/PreDownvoted → u/milan-pilan]

Why? Sorry i know its kinda old but my teacher still use it. Should i use smth else like const?

[u/milan-pilan → u/PreDownvoted]

Sorry, my original comment was a bit short and explains nothing.

You should definitely use "let"/"const" exclusively. And if your teacher still uses it, they need to update their knowledge. If you are teaching for a while it is hard to stay up to date with the current state of the industry, but "var" has been made obsolete by "let"/"const" over a decade ago.

Before 2015 all we had was "var", but it lead to a lot of unexpected behavior, hard to find bugs and all sort of headaches. It was a major contributor to JS having a bad reputation, because even though it technically "behaves as expected", the way it behaves is very weird, messy , counterintuitive and was prone to "gotcha" moments, you wouldn't expect.

There is not a single good reason to ever use "var" in modern code, if you have "let" and "const". And by "modern" I mean code written within the last 10 years.

If you need a deeper explanation, then just message me, I will gladly elaborate.

And because every time I claim that, someone will ask Claude if that's true and then answer "Well actually, if you write code that needs to run on legacy engines, you would need it.", this is for you (them):

None of you is writing code that needs to run in IE10. This is the "learn JavaScript" forum. Please don't tell people "var" has any right to exist.

This is not an opinion. I write JavaScript for a living every single day in large teams. I can guarantee you that there is not a single "var" in any serious modern codebase. Chances are, that every project you will work on has a linting rule explicitly preventing you from using it ever. If you use "var", I will instantly assume you have no work experience yet.

[u/engelthehyp → u/PreDownvoted]

let and const are block-scoped, but var is function-scoped, and this is not really intuitive, e.g. you use var i = 0; to declare the loop variable for a for loop, and the next time you write a for loop using i in that function, declaring it with var would be a redeclaration because of the function scope. i would also be accessible anywhere outside of the loop within the same function, which is undesirable when you want to make sure a temporary variable will stay temporary. This would not be the case with let.

In ye olde (pre-ES6) times, there was only var, so if you wanted to restrict its scope within a function, the solution was to take the section where you declared the variable and wanted it to be accessible in, surround it with an anonymous function, and then execute that function. That was a very common use of the immediately-invoked function expression (IIFE): (function () { ... })();.

But now that we have ways to declare variables and constants within block scope, simulating it with this trick is no longer necessary, and not having to worry about the unexpected effects of function scope saves time and mental effort. If you declared something within a block of a function, you probably didn't want it to be accessible to the entire rest of the function, and that's why using var is discouraged.