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Comment by treehau5 | Hacker News Reader

Parent literally said why in the rest of their comment. And if you still don't understand why, this probably goes back to understanding JavaScript fundamentals. Not understanding function scope vs block scope is the number one smell for me that someone did not learn JavaScript correctly.

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I don't think anything in the rest of their comment has anything to do with block scoping vs function scoping.

I do understand the technical difference very well - I have a PhD in implementing programming languages with function scoping like JavaScript.

If you agree with the person I was replying to maybe could you humour me and explain why you think function-scoping var is a useful feature?

> I do understand the technical difference very well - I have a PhD in implementing programming languages like JavaScript.

I am happy for your PhD and that it is for implementing programming languages like JavaScript.

My assertion is the advantage of having function scoping is apparent to those who understand function scoping. Block scoping-style programming in JavaScript was always, in my experienced, shoe-horned in by people who wanted to make JavaScript more like Java. That is all there is to my point.

But I do understand function scoping. I understand what it is, what its semantics are, and how to implement and use it. And the advantage over block scoping isn't apparent to me.

But even if it should be apparent to me, why can't you explain the reason to me? What is this - some kind of argument that is impossible to comprehend unless you already agree with it?

I can understand your argument that block scoping was shoe-horned into JavaScript, post hoc, but that isn't a technical argument for the benefit of function scoping, is it?

I understand your question now was more about function scoping versus block scoping from a language design perspective, and not about specific to JavaScript. It wasn't clear from your comment you were heading in that direction. Having var enable you to make use of function scoping is useful to JavaScript developers who have, up until this point in history, have always had function scoping. As parent mentioned, using var allows you define the variables where you are. It makes the code more readable. As far as function scoping versus block scoping I don't have much of a say, as I am not sure there are any meaningful advantages, merely minor ones, but none that would impact productivity if you were experienced in one or the other. Maybe you could convince me otherwise?

even if block scope was better, its not worth having three ways to declare a variable. Most JS programmers do not know about scope and they do not declare variables, but if they do, they more likely mean it to belong to the function, like in VBscript or PHP, rather then to the if statement. Explaining why you should declare variables is hard. Now I also have to explain block scope, and angel brackets now makes a huge difference!

  if(...) // use angel brackets
    foo = 1; // declare variables
  
  if(foo) ...

I really don't think that most JS programmers write code without declaring variables. Anyone using strict mode, ES6, or ESLint/JSLint/JSHint is already forced to declare variables appropriately.

Personally, I think the benefits of let are worth killing off var. I have honestly never seen an example where hoisting has been more clear than the alternative (declaring variables before they're used).

> My assertion is the advantage of having function scoping is apparent to those who understand function scoping.

I assert that if you can't say what the advantage is then you don't understand it yourself.

"You'd see the advantages if you understood this, and since you don't you must not understand it" is not a reasonable thing to say to people.

I understand it well and think relying on hoisting is a bad idea, as do most people. Declaring a var in a block and using it outside of that block (which is what hoisting enables) is the opposite of "Placing the var declarations where they are used".

Please provide an example of what you believe to be a good usage of hoisting.

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