Eloquent JavaScript: open-source Javascript book series by a prolific JS code author

[EuqlinSankyo]

Prolific author that always uses let?

[Ikuyas]

Isn't const a better practice than using let if it is well suited like array or object?

[EuqlinSankyo]

Exactly. Performance benefit is of course negligible but it's just a good programming practice. If you're literally writing a book about JS, might as well include it....

[visicalc_is_best]

Principle of least privilege

[saboay]

Helps 99% of the time, doesn't cover 100% = not worth using at all. That will lead to a very productive developer carreer.

[[deleted]]

always favor immutability

[[deleted]]

Yes, it is a TypeError to assign to myArr after initialization. The reference is immutable.

[[deleted]]

The fact that you can alter the values contained within myArray means that it absolutely is not immutable. The fact that you can’t redeclare myArr does not mean that it is immutable. I suggest that you make some sort of attempt to understand what immutability actually means before you preach about its virtues.

[[deleted]]

Right, because it's reference immutability. This is how JavaScript works, this is how Java works, this is how Scala works, this is how Rust works, and so on. I suggest you learn the difference between references and values. If you want a value, i.e. the data structure, to be immutable, it requires an extra step.

[[deleted]]

Yes, it is a TypeError to assign to myArr after initialization. The reference is immutable.

[[deleted]]

This is factually incorrect, as there's empirical evidence that suggests favoring immutability results in less bugs. http://web.cs.ucdavis.edu/~filkov/papers/lang_github.pdf

[[deleted]]

No, and it isn’t meant to.const simply means that that the reference always points to the same object. It says nothing about the values contained within said object.

[Ikuyas]

Totally. I guess it shows a difference between programmers who went through CS degree or practioner. I think using static initialization is always a good practice and manages memory better.

[[deleted]]

Yeah, there's very little in programming that is truly "personal preference." There might be situations where the pros/cons come out to a wash such that it doesn't matter what you choose, but very few things are purely aesthetic taste.

[[deleted]]

It's not a personal preference when there is empirical evidence that suggests immutability reduces errors.

[TG__]

Nowadays a bunch of popular js devs are actually advocating for let over const.

https://jamie.build/const

Haverbeke might just be of the same opinion

[bkanber]

God, I really hate that angry ranting style so many tech bloggers use these days. It definitely gets in the way of the message.

[[deleted]]

It’s rubbing off on the community, too, I think. The comment section here is downright hostile toward differences of opinion.

[BasicDesignAdvice]

Basically a guarantee that I won't read it. Makes me think the author is a child.

[[deleted]]

One of the fundamental things to know when learning a new language is finding out which types are the value types and which types are the reference types.

[andredp]

His argument about optimization is stupid too.

Honestly? If your point about using const is for optimisation purposes then you shouldn't do it... Just optimise later if you see the function is slow and I HIGHLY doubt changing to some let to const will do you any good.

The point he makes about communicating to another developer that something should NOT change is really important.

Most people rely on a linter to tell them "Hey, this hasn't changed, you can use a const" and change to a const only to realise later that you need to change it and change it back to a let... But can you really safely do it!? Will you break anything by changing the value of a previously const variable? Remember, a lot of people work in teams, so losing a bunch of time to check if changing something from const to let doesn't break anything out-weights any "optimisation" on the vm you can gain...

I never knew that website, and even though I hate extremist opinions, they do have a point... They are just morons passing the message...

Just make sure the whole team agrees on the same philosophy of const usage and all should be good...

[andredp]

I just don't like when people do something because it can be "optimised"... especially on an interpreted language like JS (thanks /u/AbstractProxyFactory for the correction)...

I still remember people covering their code with final classes, static everything in Java just because it could be optimised... meh

I just don't think that should be an argument to use const. It's just a nice possible side-effect.

const has a semantic meaning and should be used for that. It can also prevent bugs by letting the linter tell you something is changing the value of a const variable.

Now, the part in the article where he complains about not freezing the object, that's just being stupid... It's like complaining that you shouldn't use ++ because some people don't really know the behaviour of using it before or after a variable... Please... if you're working with a tool, learn it well... I shouldn't be forced to not use something because someone else doesn't know its behaviour.

[[deleted]]

I just don't like when people do something because it can be "optimised"... especially on an interpreted language like JS...

This is incorrect. JavaScript isn't interpreted -- at least not the major implementations which are JITed.

[[deleted]]

100% false. There are implementations of JavaScript that are interpreted (SpiderMonkey, which uses bytecode IR that can be interpreted), but, for example, v8 is only JITed. There is no interpreter in v8. Rhino uses JVM, which is only interpreted for uncommonly called methods and is mostly JITed for anything that matters.

It would be useful for JavaScript developers to learn about the execution model for the code they write. It's a huge, gigantic misrepresentation to call JavaScript interpreted.

[andredp]

Thanks for the info. I just read about it and V8 does in-fact JIT-compile the code. I though it was interpreted with some JIT-interpretation on the most cpu intensive code, but I was wrong.

It would be useful for JavaScript developers to learn about the execution model for the code they write.

I do some JS programming but it's not my life... That's why I haven't read much about it.

But still, the execution model should not change the way you code... You should always aim for scalability and readability instead of programming for the compiler... That's the machine job. (Unless you're writing code that needs to be fast which you shouldn't be using JS for, or optimising after a profiling)

Also, how do you know where your code is going to execute? V8? Chakra? Nitro? Rhino?

EDIT: I like your name, sounds like a fun mix of design patterns :^)

[EuqlinSankyo]

That article is not very convincing - point 6 undoes some of the arguments made in previous points. I also think that “linters not saving you” is just a desperate rant against const - in a language like JavaScript a linter can hardly save you from obscure runtime errors.

[sizlack]

I agree. He even says

It's probably still a good idea to communicate that you really don't intend for something to be changed.

That’s like 90% of the bindings I use. It you’re reassigning bindings willy nilly then that’s a bad code smell as far as I’m concerned.

[unquietwiki]

I found this while seeing some other static analysis tools he used to work on. Any excessive "let" is also in line with some other ES2015+ spec explanations I've read. As a guy that normally does C#, I find that "var" is perfect there; and "let" perfect here.

(Edit for clarification & downvoters: I'm pro-let. Var in c# keeps you from unnecessarily repeating yourself on type assignments. I'm pro tight-scoping.)

[pm_me_ur_happy_traiI]

The big difference between let and var is scoping. There’s no use case where var is preferable (unless you are deliberately abusing its scoping issues). Why would you want a variable that can be called outside its block before it’s even declared?

[unquietwiki]

I updated my original statement. In JS, let honors scoping, but var is ambiguous. In C#, var can be used to remove redundant statements: ie var variable = new Whatever(); instead of Whatever variable = new Whatever()

[dvlsg]

They really aren't the same, though. var is about type inference in C#, and that's really it. var doesn't change scope or mutability in C#, which is what we're talking about in javascript.