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What’s New in ES2019

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Re: What’s New in ES2019

#11

Post by Dextro »

afandian wrote: post #3

It's great to see JS getting some of the features of better planned languages. But I'm still very nervous about some of the stuff mentioned here with regard to mutation. Taking Rust and Clojure as references, you always know for sure whether or not a call to e.g. `flat` will result in a mutation. In JS, because of past experience, I'd never be completely confident that I wasn't mutating something by mistake. I don't…

Yes, this is a real problem and I've been bitten by it more times than I can count. Now I always keep this handy website ready: https://doesitmutate.xyz/

Re: What’s New in ES2019

#12

Post by afandian »

zachrose wrote: post #9
afandian wrote: post #3

It's great to see JS getting some of the features of better planned languages. But I'm still very nervous about some of the stuff mentioned here with regard to mutation. Taking Rust and Clojure as references, you always know for sure whether or not a call to e.g. `flat` will result in a mutation. In JS, because of past experience, I'd never be completely confident that I wasn't mutating something by mistake. I don't…

In other words you’re concerned that some Array methods mutate the array (push, pop) and some don’t (map, concat)? If so then yeah, that can be annoying and/or confusing.

Yes, it stems from arrays. But extends from there to any collection, built in or custom. Kind of bridges the built in type system but it's really about the expressivity of the language.

It becomes especially important in React where you share objects up and down an immutable structure of objects.

Re: What’s New in ES2019

#13

Post by afandian »

Dextro wrote: post #11
afandian wrote: post #3

It's great to see JS getting some of the features of better planned languages. But I'm still very nervous about some of the stuff mentioned here with regard to mutation. Taking Rust and Clojure as references, you always know for sure whether or not a call to e.g. `flat` will result in a mutation. In JS, because of past experience, I'd never be completely confident that I wasn't mutating something by mistake. I don't…

Yes, this is a real problem and I've been bitten by it more times than I can count. Now I always keep this handy website ready: https://doesitmutate.xyz/

Thanks for sharing.

I think this is the kind of thing you just have to learn when you use any language. But when you're switching between half a dozen, being able to rely on consistent founding design principles really makes things easier. And when there aren't any, this kind of guide helps.

Re: What’s New in ES2019

#14

Post by jmkni »

kuon wrote: post #6

The part about parameter less catch reveals a lot about the philosophy of the language. For me, silencing error like this is a bad practice. You may still produce a sane error in the catch, but the design goes toward silencing things. I really love languages that force you to handle errors up to the top level.

What's a good example of this sort of language?

Re: What’s New in ES2019

#15

Post by lkschubert8 »

zachrose wrote: post #9
afandian wrote: post #3

It's great to see JS getting some of the features of better planned languages. But I'm still very nervous about some of the stuff mentioned here with regard to mutation. Taking Rust and Clojure as references, you always know for sure whether or not a call to e.g. `flat` will result in a mutation. In JS, because of past experience, I'd never be completely confident that I wasn't mutating something by mistake. I don't…

In other words you’re concerned that some Array methods mutate the array (push, pop) and some don’t (map, concat)? If so then yeah, that can be annoying and/or confusing.

For me the worst is slice/splice.

Re: What’s New in ES2019

#16

Post by felixfbecker »

afandian wrote: post #3

It's great to see JS getting some of the features of better planned languages. But I'm still very nervous about some of the stuff mentioned here with regard to mutation. Taking Rust and Clojure as references, you always know for sure whether or not a call to e.g. `flat` will result in a mutation. In JS, because of past experience, I'd never be completely confident that I wasn't mutating something by mistake. I don't…

JS already has immutable objects with `Object.freeze()`.

Personally I just use TypeScript which can enforce not mutating at compile time (for the most part).

Re: What’s New in ES2019

#18

Post by iraldir »

kuon wrote: post #6

The part about parameter less catch reveals a lot about the philosophy of the language. For me, silencing error like this is a bad practice. You may still produce a sane error in the catch, but the design goes toward silencing things. I really love languages that force you to handle errors up to the top level.

It does, though I wouldn't go to the same conclusion. It gives more freedom to the developer. They are lot of cases where errors are in fact, expected. Parsing a user inputted JSON. Making a request to check internet connection availability. Any promise that is going to be consumed by an async - await pattern. In those cases (and many more), you may want to try something just simply to see if it works. It's completely different say to being on the backend, trying to write to a database which may or may not fail.

In those cases, forcing the extra parameter in the catch, even though you are not using it, is slightly annoying. I mean it's literally 3 characters, but in this age of linters encouraging to not specify arguments you don't use, it just feels unnatural.

Re: What’s New in ES2019

#19

Post by Latty »

afandian wrote: post #13
Dextro wrote: post #11

Earlier quoted context omitted.

Yes, this is a real problem and I've been bitten by it more times than I can count. Now I always keep this handy website ready: https://doesitmutate.xyz/

Thanks for sharing. I think this is the kind of thing you just have to learn when you use any language. But when you're switching between half a dozen, being able to rely on consistent founding design principles really makes things easier. And when there aren't any, this kind of guide helps.

I really like Python's design here, if we are not talking about full on language features to enforce immutability, where functions that mutate never return a value and are named with verbs (e.g. 'sort()'), while functions that don't mutate return their value and are named with adjectives (e.g. 'sorted()'). This feels natural - mutations are actions, while pure functions are descriptions.

The only real downside is the lack of return values mean you can't chain mutations, but personally that never bothered me.

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