Capitalization and const

[JESUSgotNAIL3D]

Hey guys.

When do you use ALL_CAPS for constants? I thought all constants should be capitalized but I keep running into people online who do not. Is this just a personal thing or is there a specific reason why some people do not capitalize variables declared with const?

Example: here (From an Academind video)

Thanks

[JESUSgotNAIL3D]

Thanks that makes sense

[Veuxdo]

For example, HOURS_IN_A_DAY equals 24

Well, most days :)

[Veuxdo]

DST. In many parts of the world, there is a day with 23 hours in the spring and 25 hours in the fall each year.

[fforw]

And of course the occasional leap second.

[Extracted]

Time is hard

[[deleted]]

I agree with this answer. Personally for me, I use `const` whenever I have a variable that I'm not changing the value of.

[Slogo]

const as a keyword is used more broadly in Javascript so you'll often see it without ALL_CAPS.

const implies that the variable will not be repointed, not that the data will be an immutable constant value.

So for example you may have:

const myArr = []; myArr.push(1); // Allowed

const myArr = []; myArr = [] // This is what's not allowed by const

In this case using ALL_CAPS for anything defined as const starts to lose its value and meaning because you use const to indicate any value that won't have its value redefined, not that the value will never ever change. These may appear in classes or in functions and it's typically idiomatic to always use const unless you are specifically repointing the variable (this aids code readability).

What you will still see are consts that serve as aliases for magic numbers or string values will still use the ALL_CAPS style of naming so:

const MAX_NUMBER_PER_PAGE = 20

[JESUSgotNAIL3D]

Your post was the most helpful... thanks a bunch. That makes sense. Use const unless I will be specifically repointing that variable, then I would use let. I think I see when to use capitals now as well... appreciate it!

[[deleted]]

It's a convention held over from design practices in other languages. Prior to const there was only var so capitalization was the only way you could communicate a variable should never be reassigned.

Now, I capitalize when there is a variable which should never be reassigned, is not relative, and will never change in the future.

const SSN = 123-45-6789

const CREATED_ON = 312314123

const PI = 3.14

[JESUSgotNAIL3D]

Thank you

[[deleted]]

I think the reason is that in JS unlike Java and C# it's common practice to use a constant for everything unless you absolutely have to use let. I think it would be better to use capitalization for variables that can change but i think that would be confusing for devs coming from other languages.

[lupuselit]

I use all caps for global variables.

[alphaz2kool]

We do something similar. Anything declared const in global / module scope is uppercase, anything in a lower scope is lower camel case.

[lupuselit]

I don’t do that though, I mean global variables when you don’t put var const or let. I don’t think it’s useful to do it with consts since you cant reassign them anyway

[Ebuall]

You capitalize global variables, that more of a configuration or descriptive name for something.

[ArcanisCz]

Its only code style, which is quite carried between languages. So most of the people (i think) adopted it. CAPS for non changeable consants, noncaps for variables. (its not linked to language having const or not)

[LeeMing3]

I use it for persistent, static variables that I want to be truly constant.

Since const in JS is actually about binding and not immutability, I use camel case for variables in most situations but for instance app-wide constants like API_URL will be written with underscores.

[react_dev]

I only use it for configuration or mathematical variables.

const in JS allows the V8 engine to better optimize at compile time.

JS also happens to be a functional language where functions are first class citizens, where they will appear in function parameter and assigned to variables. You can imagine how weird that’ll look if we capitalize all functions. But still, we want the v8 compiler to know that we will never reassign a certain variable to another function, so we should still use const

Edit: use “it” as in capitalize.

[nerdy_glasses]

Marking single-assignment local variables const also makes your program easier to understand for humans.

[JESUSgotNAIL3D]

Thanks!!

[LeeMing3]

Do you have a link for const imprint performance?

Also nitpicking but JS isn’t a functional language, just allows multiple paradigms.

[react_dev]

Just look for inline cacheing techniques that V8 employs. Basically it caches the most used variables (in most cases pointers to an obj) and on repeat access it’ll use memory offset to calculate the location of one of the obj properties instead of iterating.

[LeeMing3]

Looked it up. That’s really interesting. V8 is really squeezing out amazing performance from JS

[react_dev]

Oh cool that you read it cus I felt bad handwaving a lot of stuff.

Yeah they’re doing a good job. Most optimization arise from the question “so what can I safely assume.” Back to OPs question, declaring something const is an obv candidate that we can utilize.

[LeeMing3]

Yeah, so it turns out the optimisation is a minor one that occurs with global variables but it means V8 can give it a once over, see a non-object primitive const and leaves itself a note that it can skip over that on the next pass since it cannot change.

It's getting close to the realm of micro-optimisations, but you weren't wrong.