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What’s New in ES2019

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Re: What’s New in ES2019

#151

Post by bernawil »

jacobwilliamroy wrote: post #89
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…

I really like the lisp convention of using !'s to indicate mutation. Like set-car! . In javascript you kind of have to reason backwards and declare your variables as immutable (const). Though there are still some bugaboos; object fields can still be overwritten even if the object was declared with const.

const only means the variable itself can't be reassigned though, and really the main complain about mutation comes from Array methods. Like Array.pop will mutate the array and you have to do an Array.split for the last item instead if you want to keep your array.

Re: What’s New in ES2019

#152

Post by seanwilson »

heavenlyblue wrote: post #21
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…

I still don't understand why neither JSs var or let allow you to redefine the variable with the same name. I makes chaining things while debugging so much harder: let a = a.project(); let a = debug(a); let a = a.eject(); vs let a1 = a.project(); let a1d = debug(a1); let a2 = a1d.eject();

Another disadvantage of reusing the same variable name is the order of the statements is usually important and it isn't always obvious how, especially when you do this in longer functions.

When you're refactoring, you then have to be much more careful when moving lines of code of code around. With unique names, you get more of a safety net (including compile time errors if you're using something like TypeScript).

Re: What’s New in ES2019

#153

Post by Latty »

jmkni wrote: post #14
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?

Elm (https://elm-lang.org/) is a language that compiles to JavaScript that doesn't have runtime exceptions.

Re: What’s New in ES2019

#154

Post by choward »

soulofmischief wrote: post #136
tomduncalf wrote: post #119

Earlier quoted context omitted.

You mean something like x % 2 === 1? I'm a JS fan but had to admit I chuckled at the implementation of is-even: https://github.com/jonschlinkert/is-even/blob/master/index.j...

That's hilarious. What's not hilarious is that, after removing the essentially useless error-checking, is-even is literally just `(n % 2) === 1`. On one hand, JS desperately needs a standard library, on the other hand, JS devs can be so infuriatingly lazy and obtuse.

> is-even is literally just `(n % 2) === 1`

Pretty sure that tells you if a number is odd. I guess maybe there is a reason these libraries exist.

Re: What’s New in ES2019

#155

Post by untog »

qudat wrote: post #150
simias wrote: post #139

Earlier quoted context omitted.

That's not unique to JS. Some compilers took over a decade to implement C99 features. Most of us C coders were still defaulting to C89 for portability well into the late 00's. But now C99 is mainstream enough that you can (mostly) safely target it. If you never release new standards you'll never be able to use them. I realize that in JS world 4 years is basically an eternity so it's hard to project that far but I'm s…

> Regarding transpilation surely it's not as standard as you make it out to be? It's popular to be sure but handwritten javascript is not that rare nowadays, is it? If you are building a modern web "app", not a one off set of web pages, then yes, it is the standard. It would be very weird to not see a compile (transpilation) step.

It's becoming less and less necessary. If you don't care about browsers with tiny usage you can ship ES6 as-is these days. All the main browsers support ES6 modules. And HTTP2 means having all those modules in different files doesn't have the huge performance impact it once did. About the only thing left (that isn't easily solvable) is stripping comments and minifying.

Re: What’s New in ES2019

#156

Post by Jasper_ »

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…

At the same time, all this copying leads to an immense amount of garbage, which can really slow apps down with GC pauses. I really wished JavaScript had support for true immutable structures (a la Immutable.js) since these things do add up.

In my side project, which is a high performance web app, I was able to get an extra ~20fps by virtually removing all garbage created each frame. And there's a lot of ways to accidentally create garbage.

Prime example is the Iterator protocol, which creates a new object with two keys for every step of the iteration. Changing one for loop from for...of back to old-style made GC pauses happen about half as much. But you can't iterate over a Map or Set without the Iterator protocol, so now all my data structures are hand-built, or simply Arrays.

I would like to see new language features be designed with a GC cost model that isn't "GC is free!" But I doubt that JavaScript is designed for me and my sensibilities....

Re: What’s New in ES2019

#158

Post by pault »

simias wrote: post #139
mmartinson wrote: post #101

Honest question, not meant to be inflammatory. If we still need to target es5 4 years later, and transpilation is standard practice, why bother? Is the evolution of JS not directed in practice by the authors of Babel and Typescript? If no one can confidently ship this stuff for years after, what’s the incentive to even bother thinking about what is official vs a Babel supported proposal. I like the idea of idiomatic…

That's not unique to JS. Some compilers took over a decade to implement C99 features. Most of us C coders were still defaulting to C89 for portability well into the late 00's. But now C99 is mainstream enough that you can (mostly) safely target it. If you never release new standards you'll never be able to use them. I realize that in JS world 4 years is basically an eternity so it's hard to project that far but I'm s…

> It's popular to be sure but handwritten javascript is not that rare nowadays, is it?

Long time front end developer here. In the last couple of years I can't recall seeing even a single project without a build pipeline (not that they don't exist, I just haven't encountered them at my day job, first or third party).

Re: What’s New in ES2019

#159

Post by GordonS »

snek wrote: post #121
mmartinson wrote: post #101

Honest question, not meant to be inflammatory. If we still need to target es5 4 years later, and transpilation is standard practice, why bother? Is the evolution of JS not directed in practice by the authors of Babel and Typescript? If no one can confidently ship this stuff for years after, what’s the incentive to even bother thinking about what is official vs a Babel supported proposal. I like the idea of idiomatic…

You only need to target old es if you're deploying a website for a big company. Most people don't need IE6 compat. For example, people writing node apps can choose which version of node they deploy.

Maybe I'm missing something, but they said es5, not es4?

Re: What’s New in ES2019

#160

Post by pault »

untog wrote: post #155
qudat wrote: post #150

Earlier quoted context omitted.

> Regarding transpilation surely it's not as standard as you make it out to be? It's popular to be sure but handwritten javascript is not that rare nowadays, is it? If you are building a modern web "app", not a one off set of web pages, then yes, it is the standard. It would be very weird to not see a compile (transpilation) step.

It's becoming less and less necessary. If you don't care about browsers with tiny usage you can ship ES6 as-is these days. All the main browsers support ES6 modules. And HTTP2 means having all those modules in different files doesn't have the huge performance impact it once did. About the only thing left (that isn't easily solvable) is stripping comments and minifying.

While that's true, dealing with compatibility issues and making sure all of your services are using http2 is arguably more work than just using babel.
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